OS Timer wrapper review

I started reworking async-timer by extracting wrapper to low level timers that doesn't require event loop (tokio) etc and I would like someone to take a look at my crate to review unsafe code:

Repo: GitHub - DoumanAsh/os-timer: OS timers wrapper for Rust
Wrapper is very simple but there are few interesting pieces like storing traib ojbect as fat pointer due inability to use const fn with fields containing trait object.