You can use super::*; to bring all names in scope from the parent module into scope for the child module. You could also define a macro which expands to some use statements, or define a prelude module which you glob import from.
Generally, though, it's standard practice to just use what you need in the module that you need it.
general style doesn't go so drastic; it's normal to keep related functionality defined in a single file. This example is probably just an oversimplification for the purpose of posting on the forum, but it merits stating.