Factor out C-API, Python API and solver tests into their own crates

[chrjabs]

Something about dependency resolution makes this break on macos and windows but not on Linux.

[ChrisJefferson]

This is just some uninformed advice, based on hitting a similar issue (you can see people talking about it here: rust-lang/cargo#6313 )

Basically, I think, cdylibs don't work well with packages that get built multiple times, and rustsat is now built with different features in different places.

The best (again, I think) solution would be to pull the C and Python interface out into their own little package, which requires rustsat. Nothing depends on that interface package, and that should "break the cycle" (although as I say, I'm guessing here).

You could try removing cdylib and see if that at least breaks the set of broken tests, to see if that moves things in the right direction?

[chrjabs]

Thanks for the pointers, that might come in very handy. So far I wanted to keep the Python API in the main crate so that it can follow the main versioning more easily, but this might have to change then.

[chrjabs]

Looks like the cdylib is indeed the problem. I guess I'll have to factor out the external APIs indeed then. At least that seems like the cleanest solution.

[chrjabs]

To-dos before merging:

• Ignore rustsat-pyapi in release-plz
• Factor out solver unit tests into rustsat-solvertests

[chrjabs]

More To-dos:

• Add basic tests to the python API