Improve the use of modules from Rust

[fpgmaas]

Is your feature request related to a problem? Please describe.

Currently, all functions and code that are made available from Rust to Python by pyo3 end up in deptry.rust, e.g.

from deptry.rust import Location

However, we might want to add submodules so we could do e.g.

from deptry.rust.imports import Location