Neli broken after changing neli-proc-macro to use syn 2.x

For reasons I cannot control, I had to change neli-proc-macro to use syn 2.x. Updated it in Cargo.toml, went piece by piece making it work, and it does. The issue is that now neli is completely broken and won't build, giving dozens if not hundreds of errors (below) that seem to not have anything to do with what I changed.
I'm looking for some tips here on how to find what made this break. I can't seem to locate where this came from, so any tips are welcome.

   Compiling neli v0.6.1 (/home/eduardo/devbox/neli)
error: proc-macro derive panicked
  --> src/err.rs:44:47
   |
44 | #[derive(Debug, PartialEq, Eq, Size, ToBytes, FromBytesWithInput, Header)]
   |                                               ^^^^^^^^^^^^^^^^^^
   |
   = help: message: "T: TypeSize + FromBytes" should be valid tokens of type syn::generics::TypeParam

error: proc-macro derive panicked
  --> src/err.rs:44:67
   |
44 | #[derive(Debug, PartialEq, Eq, Size, ToBytes, FromBytesWithInput, Header)]
   |                                                                   ^^^^^^
   |
   = help: message: "T: TypeSize" should be valid tokens of type syn::generics::TypeParam

error: proc-macro derive panicked
  --> src/err.rs:66:38
   |
66 | #[derive(Debug, PartialEq, Eq, Size, FromBytesWithInput, ToBytes, Header)]
   |                                      ^^^^^^^^^^^^^^^^^^
   |
   = help: message: "T: NlType" should be valid tokens of type syn::generics::TypeParam

error: proc-macro derive panicked
  --> src/genl.rs:39:38
   |
39 | #[derive(Debug, PartialEq, Eq, Size, ToBytes, FromBytesWithInput, Header)]
   |                                      ^^^^^^^
   |
   = help: message: "C: Cmd" should be valid tokens of type syn::generics::TypeParam

error: proc-macro derive panicked
  --> src/genl.rs:39:47
   |
39 | #[derive(Debug, PartialEq, Eq, Size, ToBytes, FromBytesWithInput, Header)]
   |                                               ^^^^^^^^^^^^^^^^^^
   |
   = help: message: "C: Cmd + TypeSize" should be valid tokens of type syn::generics::TypeParam

error: proc-macro derive panicked
  --> src/genl.rs:39:67
   |
39 | #[derive(Debug, PartialEq, Eq, Size, ToBytes, FromBytesWithInput, Header)]
   |                                                                   ^^^^^^
   |
   = help: message: "C: TypeSize" should be valid tokens of type syn::generics::TypeParam

error: proc-macro derive panicked
   --> src/genl.rs:196:38
    |
196 | #[derive(Debug, PartialEq, Eq, Size, FromBytes, ToBytes, Header)]
    |                                      ^^^^^^^^^
    |
    = help: message: "T: NlAttrType" should be valid tokens of type syn::generics::TypeParam

error: proc-macro derive panicked
   --> src/genl.rs:196:49
    |
196 | #[derive(Debug, PartialEq, Eq, Size, FromBytes, ToBytes, Header)]
    |                                                 ^^^^^^^
    |
    = help: message: "T: NlAttrType" should be valid tokens of type syn::generics::TypeParam

error: proc-macro derive panicked
   --> src/genl.rs:196:58
    |
196 | #[derive(Debug, PartialEq, Eq, Size, FromBytes, ToBytes, Header)]
    |                                                          ^^^^^^
    |
    = help: message: "T: TypeSize" should be valid tokens of type syn::generics::TypeParam

error: proc-macro derive panicked
   --> src/nl.rs:127:47
    |
127 | #[derive(Debug, PartialEq, Eq, Size, ToBytes, FromBytes, Header)]
    |                                               ^^^^^^^^^
    |
    = help: message: "T: NlType" should be valid tokens of type syn::generics::TypeParam

error: proc-macro derive panicked
   --> src/nl.rs:127:58
    |
127 | #[derive(Debug, PartialEq, Eq, Size, ToBytes, FromBytes, Header)]
    |                                                          ^^^^^^
    |
    = help: message: "T: TypeSize" should be valid tokens of type syn::generics::TypeParam

error: proc-macro derive panicked
   --> src/rtnl.rs:255:32
    |
255 | #[derive(Debug, Size, ToBytes, FromBytes, Header)]
    |                                ^^^^^^^^^
    |
    = help: message: "T: RtaType" should be valid tokens of type syn::generics::TypeParam

error: proc-macro derive panicked
   --> src/rtnl.rs:255:43
    |
255 | #[derive(Debug, Size, ToBytes, FromBytes, Header)]
    |                                           ^^^^^^
    |
    = help: message: "T: RtaType" should be valid tokens of type syn::generics::TypeParam

error: proc-macro derive panicked
  --> src/types.rs:91:38
   |
91 | #[derive(Debug, PartialEq, Eq, Size, FromBytesWithInput, ToBytes)]
   |                                      ^^^^^^^^^^^^^^^^^^
   |
   = help: message: "T: NlType" should be valid tokens of type syn::generics::TypeParam

error: proc-macro derive panicked
   --> src/types.rs:166:32
    |
166 | #[derive(Debug, PartialEq, Eq, ToBytes, FromBytesWithInput)]
    |                                ^^^^^^^
    |
    = help: message: "T: NlAttrType" should be valid tokens of type syn::generics::TypeParam

error: proc-macro derive panicked
   --> src/types.rs:166:41
    |
166 | #[derive(Debug, PartialEq, Eq, ToBytes, FromBytesWithInput)]
    |                                         ^^^^^^^^^^^^^^^^^^
    |
    = help: message: "T: NlAttrType" should be valid tokens of type syn::generics::TypeParam

error: proc-macro derive panicked
   --> src/types.rs:272:17
    |
272 | #[derive(Debug, FromBytesWithInput, ToBytes)]
    |                 ^^^^^^^^^^^^^^^^^^
    |
    = help: message: "T: RtaType" should be valid tokens of type syn::generics::TypeParam

error: proc-macro derive panicked
   --> src/types.rs:379:47
    |
379 | #[derive(Debug, PartialEq, Eq, Size, ToBytes, FromBytes)]
    |                                               ^^^^^^^^^
    |
    = help: message: "B: FromBytes + TypeSize + Debug" should be valid tokens of type syn::generics::TypeParam

warning: unused imports: `genl::NlAttrType`, `nl::NlType`, `rtnl::RtaType`
  --> src/types.rs:21:14
   |
21 |     consts::{genl::NlAttrType, nl::NlType, rtnl::RtaType},
   |              ^^^^^^^^^^^^^^^^  ^^^^^^^^^^  ^^^^^^^^^^^^^
   |
   = note: `#[warn(unused_imports)]` on by default

error[E0277]: the trait bound `FlagBuffer<u16, consts::nl::NlmF>: FromBytes<'lifetime>` is not satisfied
   --> src/consts/macros.rs:215:27
    |
215 |           $vis struct $name($crate::types::FlagBuffer::<$bin_type, $type>);
    |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `FromBytes<'lifetime>` is not implemented for `FlagBuffer<u16, consts::nl::NlmF>`
    |
   ::: src/consts/nl.rs:61:1
    |
61  | / impl_flags!(
62  | |     #[allow(missing_docs)]
63  | |     pub NlmFFlags, NlmF, u16
64  | | );
    | |_- in this macro invocation
    |
    = help: the following other types implement trait `FromBytes<'a>`:
              <() as FromBytes<'lt>>
              <Af as FromBytes<'lt>>
              <AttrType<T> as FromBytes<'lt>>
              <BeU64 as FromBytes<'a>>
              <IfaF as FromBytes<'lt>>
              <IflaInfo as FromBytes<'lt>>
              <LogCfgCmdWrapper as FromBytes<'lt>>
              <LogCmd as FromBytes<'lt>>
            and 52 others
    = note: this error originates in the macro `impl_flags` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `FlagBuffer<u32, consts::rtnl::Iff>: FromBytes<'lifetime>` is not satisfied
   --> src/consts/macros.rs:215:27
    |
215 |           $vis struct $name($crate::types::FlagBuffer::<$bin_type, $type>);
    |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `FromBytes<'lifetime>` is not implemented for `FlagBuffer<u32, consts::rtnl::Iff>`
    |
   ::: src/consts/rtnl.rs:383:1
    |
383 | / impl_flags!(
384 | |     #[allow(missing_docs)]
385 | |     pub IffFlags, Iff, libc::c_uint
386 | | );
    | |_- in this macro invocation
    |
    = help: the following other types implement trait `FromBytes<'a>`:
              <() as FromBytes<'lt>>
              <Af as FromBytes<'lt>>
              <AttrType<T> as FromBytes<'lt>>
              <BeU64 as FromBytes<'a>>
              <IfaF as FromBytes<'lt>>
              <IflaInfo as FromBytes<'lt>>
              <LogCfgCmdWrapper as FromBytes<'lt>>
              <LogCmd as FromBytes<'lt>>
            and 52 others
    = note: this error originates in the macro `impl_flags` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `FlagBuffer<u8, IfaF>: FromBytes<'lifetime>` is not satisfied
   --> src/consts/macros.rs:215:27
    |
215 |           $vis struct $name($crate::types::FlagBuffer::<$bin_type, $type>);
    |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `FromBytes<'lifetime>` is not implemented for `FlagBuffer<u8, IfaF>`
    |
   ::: src/consts/rtnl.rs:388:1
    |
388 | / impl_flags!(
389 | |     #[allow(missing_docs)]
390 | |     pub IfaFFlags, IfaF, libc::c_uchar
391 | | );
    | |_- in this macro invocation
    |
    = help: the following other types implement trait `FromBytes<'a>`:
              <() as FromBytes<'lt>>
              <Af as FromBytes<'lt>>
              <AttrType<T> as FromBytes<'lt>>
              <BeU64 as FromBytes<'a>>
              <IfaF as FromBytes<'lt>>
              <IflaInfo as FromBytes<'lt>>
              <LogCfgCmdWrapper as FromBytes<'lt>>
              <LogCmd as FromBytes<'lt>>
            and 52 others
    = note: this error originates in the macro `impl_flags` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `FlagBuffer<u32, RtmF>: FromBytes<'lifetime>` is not satisfied
   --> src/consts/macros.rs:215:27
    |
215 |           $vis struct $name($crate::types::FlagBuffer::<$bin_type, $type>);
    |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `FromBytes<'lifetime>` is not implemented for `FlagBuffer<u32, RtmF>`
    |
   ::: src/consts/rtnl.rs:393:1
    |
393 | / impl_flags!(
394 | |     #[allow(missing_docs)]
395 | |     pub RtmFFlags, RtmF, libc::c_uint
396 | | );
    | |_- in this macro invocation
    |
    = help: the following other types implement trait `FromBytes<'a>`:
              <() as FromBytes<'lt>>
              <Af as FromBytes<'lt>>
              <AttrType<T> as FromBytes<'lt>>
              <BeU64 as FromBytes<'a>>
              <IfaF as FromBytes<'lt>>
              <IflaInfo as FromBytes<'lt>>
              <LogCfgCmdWrapper as FromBytes<'lt>>
              <LogCmd as FromBytes<'lt>>
            and 52 others
    = note: this error originates in the macro `impl_flags` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `FlagBuffer<u16, Nud>: FromBytes<'lifetime>` is not satisfied
   --> src/consts/macros.rs:215:27
    |
215 |           $vis struct $name($crate::types::FlagBuffer::<$bin_type, $type>);
    |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `FromBytes<'lifetime>` is not implemented for `FlagBuffer<u16, Nud>`
    |
   ::: src/consts/rtnl.rs:397:1
    |
397 | / impl_flags!(
398 | |     #[allow(missing_docs)]
399 | |     pub NudFlags, Nud, u16
400 | | );
    | |_- in this macro invocation
    |
    = help: the following other types implement trait `FromBytes<'a>`:
              <() as FromBytes<'lt>>
              <Af as FromBytes<'lt>>
              <AttrType<T> as FromBytes<'lt>>
              <BeU64 as FromBytes<'a>>
              <IfaF as FromBytes<'lt>>
              <IflaInfo as FromBytes<'lt>>
              <LogCfgCmdWrapper as FromBytes<'lt>>
              <LogCmd as FromBytes<'lt>>
            and 52 others
    = note: this error originates in the macro `impl_flags` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `FlagBuffer<u8, Ntf>: FromBytes<'lifetime>` is not satisfied
   --> src/consts/macros.rs:215:27
    |
215 |           $vis struct $name($crate::types::FlagBuffer::<$bin_type, $type>);
    |                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `FromBytes<'lifetime>` is not implemented for `FlagBuffer<u8, Ntf>`
    |
   ::: src/consts/rtnl.rs:401:1
    |
401 | / impl_flags!(
402 | |     #[allow(missing_docs)]
403 | |     pub NtfFlags, Ntf, u8
404 | | );
    | |_- in this macro invocation
    |
    = help: the following other types implement trait `FromBytes<'a>`:
              <() as FromBytes<'lt>>
              <Af as FromBytes<'lt>>
              <AttrType<T> as FromBytes<'lt>>
              <BeU64 as FromBytes<'a>>
              <IfaF as FromBytes<'lt>>
              <IflaInfo as FromBytes<'lt>>
              <LogCfgCmdWrapper as FromBytes<'lt>>
              <LogCmd as FromBytes<'lt>>
            and 52 others
    = note: this error originates in the macro `impl_flags` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0599]: no function or associated item named `header_size` found for struct `Nlattr` in the current scope
   --> src/genl.rs:228:28
    |
202 | pub struct Nlattr<T, P> {
    | ----------------------- function or associated item `header_size` not found for this struct
...
228 |             nla_len: Self::header_size() as u16,
    |                            ^^^^^^^^^^^ function or associated item not found in `Nlattr<T, Buffer>`
    |
note: if you're trying to build a new `Nlattr<T, Buffer>`, consider using `Nlattr::<T, Buffer>::new` which returns `Result<Nlattr<_, Buffer>, SerError>`
   --> src/genl.rs:218:5
    |
218 | /     pub fn new<P>(
219 | |         nla_nested: bool,
220 | |         nla_network_order: bool,
221 | |         nla_type: T,
...   |
224 | |     where
225 | |         P: Size + ToBytes,
    | |__________________________^
    = help: items from traits can only be used if the trait is implemented and in scope
note: `Header` defines an item `header_size`, perhaps you need to implement it
   --> src/lib.rs:244:1
    |
244 | pub trait Header {
    | ^^^^^^^^^^^^^^^^

error[E0599]: no method named `to_bytes` found for reference `&Nlattr<TT, P>` in the current scope
   --> src/genl.rs:247:14
    |
247 |         attr.to_bytes(&mut buffer)?;
    |              ^^^^^^^^ method not found in `&Nlattr<TT, P>`
    |
    = help: items from traits can only be used if the trait is implemented and in scope
note: `ToBytes` defines an item `to_bytes`, perhaps you need to implement it
   --> src/lib.rs:198:1
    |
198 | pub trait ToBytes: Debug {
    | ^^^^^^^^^^^^^^^^^^^^^^^^
help: some of the expressions' fields have a method of the same name
    |
247 |         attr.nla_len.to_bytes(&mut buffer)?;
    |              ++++++++
247 |         attr.nla_payload.to_bytes(&mut buffer)?;
    |              ++++++++++++
247 |         attr.nla_type.to_bytes(&mut buffer)?;
    |              +++++++++

error[E0599]: no function or associated item named `from_bytes_with_input` found for struct `GenlBuffer` in the current scope
   --> src/genl.rs:259:40
    |
259 |         Ok(AttrHandle::new(GenlBuffer::from_bytes_with_input(
    |                                        ^^^^^^^^^^^^^^^^^^^^^ function or associated item not found in `GenlBuffer<_, _>`
    |
   ::: src/types.rs:170:1
    |
170 | pub struct GenlBuffer<T, P>(#[neli(input)] Vec<Nlattr<T, P>>);
    | --------------------------- function or associated item `from_bytes_with_input` not found for this struct
    |
note: if you're trying to build a new `GenlBuffer<_, _>`, consider using `GenlBuffer::<T, P>::new` which returns `GenlBuffer<_, _>`
   --> src/types.rs:228:5
    |
228 |     pub fn new() -> Self {
    |     ^^^^^^^^^^^^^^^^^^^^
    = help: items from traits can only be used if the trait is implemented and in scope
note: `FromBytesWithInput` defines an item `from_bytes_with_input`, perhaps you need to implement it
   --> src/lib.rs:231:1
    |
231 | pub trait FromBytesWithInput<'a>: Sized + Debug {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0599]: no function or associated item named `from_bytes_with_input` found for struct `GenlBuffer` in the current scope
   --> src/genl.rs:270:43
    |
270 |         Ok(AttrHandleMut::new(GenlBuffer::from_bytes_with_input(
    |                                           ^^^^^^^^^^^^^^^^^^^^^ function or associated item not found in `GenlBuffer<_, _>`
    |
   ::: src/types.rs:170:1
    |
170 | pub struct GenlBuffer<T, P>(#[neli(input)] Vec<Nlattr<T, P>>);
    | --------------------------- function or associated item `from_bytes_with_input` not found for this struct
    |
note: if you're trying to build a new `GenlBuffer<_, _>`, consider using `GenlBuffer::<T, P>::new` which returns `GenlBuffer<_, _>`
   --> src/types.rs:228:5
    |
228 |     pub fn new() -> Self {
    |     ^^^^^^^^^^^^^^^^^^^^
    = help: items from traits can only be used if the trait is implemented and in scope
note: `FromBytesWithInput` defines an item `from_bytes_with_input`, perhaps you need to implement it
   --> src/lib.rs:231:1
    |
231 | pub trait FromBytesWithInput<'a>: Sized + Debug {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0599]: no function or associated item named `from_bytes_with_input` found for struct `GenlBuffer` in the current scope
   --> src/genl.rs:318:40
    |
318 |         Ok(AttrHandle::new(GenlBuffer::from_bytes_with_input(
    |                                        ^^^^^^^^^^^^^^^^^^^^^ function or associated item not found in `GenlBuffer<_, _>`
    |
   ::: src/types.rs:170:1
    |
170 | pub struct GenlBuffer<T, P>(#[neli(input)] Vec<Nlattr<T, P>>);
    | --------------------------- function or associated item `from_bytes_with_input` not found for this struct
    |
note: if you're trying to build a new `GenlBuffer<_, _>`, consider using `GenlBuffer::<T, P>::new` which returns `GenlBuffer<_, _>`
   --> src/types.rs:228:5
    |
228 |     pub fn new() -> Self {
    |     ^^^^^^^^^^^^^^^^^^^^
    = help: items from traits can only be used if the trait is implemented and in scope
note: `FromBytesWithInput` defines an item `from_bytes_with_input`, perhaps you need to implement it
   --> src/lib.rs:231:1
    |
231 | pub trait FromBytesWithInput<'a>: Sized + Debug {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0599]: no function or associated item named `from_bytes_with_input` found for struct `NlmsghdrErr` in the current scope
   --> src/nl.rs:92:56
    |
92  |                         let ok = NlmsghdrErr::<T, ()>::from_bytes_with_input(
    |                                                        ^^^^^^^^^^^^^^^^^^^^^ function or associated item not found in `NlmsghdrErr<T, ()>`
    |
   ::: src/err.rs:48:1
    |
48  | pub struct NlmsghdrErr<T, P> {
    | ---------------------------- function or associated item `from_bytes_with_input` not found for this struct
    |
    = help: items from traits can only be used if the trait is implemented and in scope
note: `FromBytesWithInput` defines an item `from_bytes_with_input`, perhaps you need to implement it
   --> src/lib.rs:231:1
    |
231 | pub trait FromBytesWithInput<'a>: Sized + Debug {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0599]: no function or associated item named `from_bytes_with_input` found for struct `NlmsghdrErr` in the current scope
   --> src/nl.rs:109:55
    |
109 |                         let ok = NlmsghdrErr::<T, P>::from_bytes_with_input(
    |                                                       ^^^^^^^^^^^^^^^^^^^^^ function or associated item not found in `NlmsghdrErr<T, P>`
    |
   ::: src/err.rs:48:1
    |
48  | pub struct NlmsghdrErr<T, P> {
    | ---------------------------- function or associated item `from_bytes_with_input` not found for this struct
    |
    = help: items from traits can only be used if the trait is implemented and in scope
note: `FromBytesWithInput` defines an item `from_bytes_with_input`, perhaps you need to implement it
   --> src/lib.rs:231:1
    |
231 | pub trait FromBytesWithInput<'a>: Sized + Debug {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0277]: cannot add `&str` to `usize`
  --> src/rtnl.rs:24:32
   |
24 | #[derive(Debug, Size, ToBytes, FromBytesWithInput, Header)]
   |                                ^^^^^^^^^^^^^^^^^^ no implementation for `usize + &str`
   |
   = help: the trait `Add<&str>` is not implemented for `usize`
   = help: the following other types implement trait `Add<Rhs>`:
             <&'a usize as Add<usize>>
             <&usize as Add<&usize>>
             <usize as Add<&usize>>
             <usize as Add>
   = note: this error originates in the derive macro `FromBytesWithInput` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `RtBuffer<consts::rtnl::Ifla, Buffer>: FromBytesWithInput<'lifetime>` is not satisfied
  --> src/rtnl.rs:39:18
   |
39 |     pub rtattrs: RtBuffer<Ifla, Buffer>,
   |                  ^^^^^^^^^^^^^^^^^^^^^^ the trait `FromBytesWithInput<'lifetime>` is not implemented for `RtBuffer<consts::rtnl::Ifla, Buffer>`
   |
   = help: the following other types implement trait `FromBytesWithInput<'a>`:
             <&'a [u8] as FromBytesWithInput<'a>>
             <&'a str as FromBytesWithInput<'a>>
             <() as FromBytesWithInput<'lt>>
             <Buffer as FromBytesWithInput<'lifetime>>
             <Ifaddrmsg as FromBytesWithInput<'lifetime>>
             <Ifinfomsg as FromBytesWithInput<'lifetime>>
             <Ndmsg as FromBytesWithInput<'lifetime>>
             <NlPayload<T, P> as FromBytesWithInput<'a>>
           and 4 others

error[E0277]: the trait bound `RtBuffer<consts::rtnl::Ifla, Buffer>: FromBytesWithInput<'lifetime>` is not satisfied
  --> src/rtnl.rs:24:32
   |
24 | #[derive(Debug, Size, ToBytes, FromBytesWithInput, Header)]
   |                                ^^^^^^^^^^^^^^^^^^ the trait `FromBytesWithInput<'lifetime>` is not implemented for `RtBuffer<consts::rtnl::Ifla, Buffer>`
   |
   = help: the following other types implement trait `FromBytesWithInput<'a>`:
             <&'a [u8] as FromBytesWithInput<'a>>
             <&'a str as FromBytesWithInput<'a>>
             <() as FromBytesWithInput<'lt>>
             <Buffer as FromBytesWithInput<'lifetime>>
             <Ifaddrmsg as FromBytesWithInput<'lifetime>>
             <Ifinfomsg as FromBytesWithInput<'lifetime>>
             <Ndmsg as FromBytesWithInput<'lifetime>>
             <NlPayload<T, P> as FromBytesWithInput<'a>>
           and 4 others
   = note: this error originates in the derive macro `FromBytesWithInput` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: cannot add `&str` to `usize`
   --> src/rtnl.rs:103:32
    |
103 | #[derive(Debug, Size, ToBytes, FromBytesWithInput, Header)]
    |                                ^^^^^^^^^^^^^^^^^^ no implementation for `usize + &str`
    |
    = help: the trait `Add<&str>` is not implemented for `usize`
    = help: the following other types implement trait `Add<Rhs>`:
              <&'a usize as Add<usize>>
              <&usize as Add<&usize>>
              <usize as Add<&usize>>
              <usize as Add>
    = note: this error originates in the derive macro `FromBytesWithInput` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `RtBuffer<consts::rtnl::Ifa, Buffer>: FromBytesWithInput<'lifetime>` is not satisfied
   --> src/rtnl.rs:117:18
    |
117 |     pub rtattrs: RtBuffer<Ifa, Buffer>,
    |                  ^^^^^^^^^^^^^^^^^^^^^ the trait `FromBytesWithInput<'lifetime>` is not implemented for `RtBuffer<consts::rtnl::Ifa, Buffer>`
    |
    = help: the following other types implement trait `FromBytesWithInput<'a>`:
              <&'a [u8] as FromBytesWithInput<'a>>
              <&'a str as FromBytesWithInput<'a>>
              <() as FromBytesWithInput<'lt>>
              <Buffer as FromBytesWithInput<'lifetime>>
              <Ifaddrmsg as FromBytesWithInput<'lifetime>>
              <Ifinfomsg as FromBytesWithInput<'lifetime>>
              <Ndmsg as FromBytesWithInput<'lifetime>>
              <NlPayload<T, P> as FromBytesWithInput<'a>>
            and 4 others

error[E0277]: the trait bound `RtBuffer<consts::rtnl::Ifa, Buffer>: FromBytesWithInput<'lifetime>` is not satisfied
   --> src/rtnl.rs:103:32
    |
103 | #[derive(Debug, Size, ToBytes, FromBytesWithInput, Header)]
    |                                ^^^^^^^^^^^^^^^^^^ the trait `FromBytesWithInput<'lifetime>` is not implemented for `RtBuffer<consts::rtnl::Ifa, Buffer>`
    |
    = help: the following other types implement trait `FromBytesWithInput<'a>`:
              <&'a [u8] as FromBytesWithInput<'a>>
              <&'a str as FromBytesWithInput<'a>>
              <() as FromBytesWithInput<'lt>>
              <Buffer as FromBytesWithInput<'lifetime>>
              <Ifaddrmsg as FromBytesWithInput<'lifetime>>
              <Ifinfomsg as FromBytesWithInput<'lifetime>>
              <Ndmsg as FromBytesWithInput<'lifetime>>
              <NlPayload<T, P> as FromBytesWithInput<'a>>
            and 4 others
    = note: this error originates in the derive macro `FromBytesWithInput` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: cannot add `&str` to `usize`
   --> src/rtnl.rs:129:32
    |
129 | #[derive(Debug, Size, ToBytes, FromBytesWithInput, Header)]
    |                                ^^^^^^^^^^^^^^^^^^ no implementation for `usize + &str`
    |
    = help: the trait `Add<&str>` is not implemented for `usize`
    = help: the following other types implement trait `Add<Rhs>`:
              <&'a usize as Add<usize>>
              <&usize as Add<&usize>>
              <usize as Add<&usize>>
              <usize as Add>
    = note: this error originates in the derive macro `FromBytesWithInput` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0277]: the trait bound `for<'b> Genlmsghdr<consts::genl::CtrlCmd, consts::genl::CtrlAttr>: FromBytesWithInput<'b>` is not satisfied
   --> src/socket.rs:491:24
    |
491 |         for res_msg in self.iter::<GenlId, Genlmsghdr<CtrlCmd, CtrlAttr>>(false) {
    |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `for<'b> FromBytesWithInput<'b>` is not implemented for `Genlmsghdr<consts::genl::CtrlCmd, consts::genl::CtrlAttr>`, which is required by `NlMessageIter<'_, consts::nl::GenlId, Genlmsghdr<consts::genl::CtrlCmd, consts::genl::CtrlAttr>>: IntoIterator`
    |
    = help: the following other types implement trait `FromBytesWithInput<'a>`:
              <&'a [u8] as FromBytesWithInput<'a>>
              <&'a str as FromBytesWithInput<'a>>
              <() as FromBytesWithInput<'lt>>
              <Buffer as FromBytesWithInput<'lifetime>>
              <Ifaddrmsg as FromBytesWithInput<'lifetime>>
              <Ifinfomsg as FromBytesWithInput<'lifetime>>
              <Ndmsg as FromBytesWithInput<'lifetime>>
              <NlPayload<T, P> as FromBytesWithInput<'a>>
            and 4 others
note: required for `NlMessageIter<'_, consts::nl::GenlId, Genlmsghdr<consts::genl::CtrlCmd, consts::genl::CtrlAttr>>` to implement `Iterator`
   --> src/iter.rs:114:16
    |
114 | impl<'a, T, P> Iterator for NlMessageIter<'a, T, P>
    |                ^^^^^^^^     ^^^^^^^^^^^^^^^^^^^^^^^
...
117 |     P: for<'b> FromBytesWithInput<'b, Input = usize> + Debug,
    |        --------------------------------------------- unsatisfied trait bound introduced here
    = note: required for `NlMessageIter<'_, consts::nl::GenlId, Genlmsghdr<consts::genl::CtrlCmd, consts::genl::CtrlAttr>>` to implement `IntoIterator`

error[E0599]: no function or associated item named `from_bytes` found for struct `Nlmsghdr` in the current scope
   --> src/socket.rs:584:64
    |
584 |             let deserialized_packet_result = Nlmsghdr::<T, P>::from_bytes(&mut Cursor::new(
    |                                                                ^^^^^^^^^^ function or associated item not found in `Nlmsghdr<T, P>`
    |
   ::: src/nl.rs:132:1
    |
132 | pub struct Nlmsghdr<T, P> {
    | ------------------------- function or associated item `from_bytes` not found for this struct
    |
note: if you're trying to build a new `Nlmsghdr<T, P>`, consider using `Nlmsghdr::<T, P>::new` which returns `Nlmsghdr<_, _>`
   --> src/nl.rs:156:5
    |
156 | /     pub fn new(
157 | |         nl_len: Option<u32>,
158 | |         nl_type: T,
159 | |         nl_flags: NlmFFlags,
...   |
162 | |         nl_payload: NlPayload<T, P>,
163 | |     ) -> Self {
    | |_____________^
    = help: items from traits can only be used if the trait is implemented and in scope
    = note: the following traits define an item `from_bytes`, perhaps you need to implement one of them:
            candidate #1: `FromBytes`
            candidate #2: `OsStrExt`

error[E0599]: no function or associated item named `from_bytes_with_input` found for struct `NlBuffer` in the current scope
   --> src/socket.rs:643:23
    |
643 |             NlBuffer::from_bytes_with_input(&mut Cursor::new(&self.buffer[0..self.end]), self.end)?;
    |                       ^^^^^^^^^^^^^^^^^^^^^ function or associated item not found in `NlBuffer<_, _>`
    |
   ::: src/types.rs:94:1
    |
94  | pub struct NlBuffer<T, P>(#[neli(input)] Vec<Nlmsghdr<T, P>>);
    | ------------------------- function or associated item `from_bytes_with_input` not found for this struct
    |
note: if you're trying to build a new `NlBuffer<_, _>`, consider using `NlBuffer::<T, P>::new` which returns `NlBuffer<_, _>`
   --> src/types.rs:113:5
    |
113 |     pub fn new() -> Self {
    |     ^^^^^^^^^^^^^^^^^^^^
    = help: items from traits can only be used if the trait is implemented and in scope
note: `FromBytesWithInput` defines an item `from_bytes_with_input`, perhaps you need to implement it
   --> src/lib.rs:231:1
    |
231 | pub trait FromBytesWithInput<'a>: Sized + Debug {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

warning: unused import: `TypeSize`
  --> src/err.rs:35:59
   |
35 |     FromBytes, FromBytesWithInput, Header, Size, ToBytes, TypeSize,
   |                                                           ^^^^^^^^

warning: unused import: `FromBytes`
  --> src/socket.rs:52:5
   |
52 |     FromBytes, FromBytesWithInput, ToBytes,
   |     ^^^^^^^^^

warning: unused import: `NlType`
  --> src/err.rs:33:18
   |
33 |     consts::nl::{NlType, NlmFFlags},
   |                  ^^^^^^

warning: unused import: `FromBytes`
  --> src/err.rs:35:5
   |
35 |     FromBytes, FromBytesWithInput, Header, Size, ToBytes, TypeSize,
   |     ^^^^^^^^^

Some errors have detailed explanations: E0277, E0599.
For more information about an error, try `rustc --explain E0277`.
warning: `neli` (lib) generated 5 warnings
error: could not compile `neli` (lib) due to 58 previous errors; 5 warnings emitted

I can't be certain, but I've only seen such "weird" issues when multiple versions of a dependency get introduced and types from one version get passed to code expecting types from another version. Hopefully that gives a direction to troubleshoot.