> Correct use, documentation, and other concerns are important for all libraries, whether got via cargo or otherwise

This is true.

However the Cargo/Rust ecosystem has one standard answer, read the associated crate docs, e.g.:

https://docs.rs/libloading

Coincidentally, the above linked crate `libloading` also shows how to access functionality in a shared library that exposes a C ABI compatible interface whatever the implementation language.