Add additional model tests

[cthoyt]

Summary

This PR adds tests to make sure that all models inherit from the correct base class, that their arguments are kwarg only, and that there are defaults for all arguments.

• [ ] Code passes all tests
• [x] Unit tests provided for these changes
• [x] Documentation and docstrings added for these changes

Changes

• add test for inheritance
• add test for arguments

Additional remarks

This PR doesn't go as far as to check that all submodules from chemicalx.models are imported somewhere in chemicalx/models/__init__.py. We can leave that for checking manually during review, since all people making PRs for models should have them exposed before the PR can be accepted

[codecov-commenter]

Codecov Report

Merging #46 (fb7fb7d) into main (6ac8eb3) will increase coverage by 0.03%. The diff coverage is 100.00%.

:exclamation: Current head fb7fb7d differs from pull request most recent head 6d2cc97. Consider uploading reports for the commit 6d2cc97 to get more accurate results

@@            Coverage Diff             @@
##             main      #46      +/-   ##
==========================================
+ Coverage   98.64%   98.68%   +0.03%     
==========================================
  Files          27       27              
  Lines         664      682      +18     
==========================================
+ Hits          655      673      +18     
  Misses          9        9              

Impacted Files	Coverage Δ
tests/unit/test_models.py	100.00% <100.00%> (ø)

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