Expanding test cases

[ijpulidos]

We have some tests running in the CI, but since atom mapping could have so many corner cases I think it's valuable that we expand the tests for the atom mapper to more of these. This issue is intended at discussing which cases are desired to be tested. As far as I can think of, we would like to have at least the following tests that are related to protein/residue mutations.

• Different capped AAs mapping. Some "key" cases and check that the mapped atoms are the expected ones.
• Full protein mappings. Maybe a tyk2 with a mutated tyk2 or similar.
• Mapping of proteins (or big molecules) on itself, we would expect every atom to be mapped.
• Mapping big protein to small peptides/AAs or vice versa.

As usual more than coverage we want more test cases, so I think this is something somewhat desired. One caveat is that some of these tests could take a few minutes to make the whole mapping. But this could also be helpful to do benchmarking on our current implementation.