Bug: handle duplicated dependencies

[Nadrieril]

Rust can handle a single dependency crate appearing many times with different versions. I suspect we don't handle this correctly in names. Either way we should at least have a test.

[Nadrieril]

This issue most importantly requires a test to be added in tests/cargo, where two crates with the same name end up in the crate graph, and we extract items from both. Ideally the test should only involve tiny crates created for that purpose. I don't know exactly how to make cargo accept this however, experimentation will be needed.

If local crates don't work, I know that cargo allows multiple versions of a same crate to coexist in a same crate graph. So we could do it with real crates.