Remove nosetest and convert tests to pytest

[mplough-kobold]

Previously the Makefile ran tests using nosetests but CI ran tests using pytest. Nose is very old; the last release on PyPI is 1.3.7 from June 2015.

As pytest provides excellent test tooling, this PR transitions tests, documentation, and support tooling to use only pytest. Tests written in unittest.TestCase style have transitioned to use pytest's xunit support.

As tests/test_Scipy.py did include any class-level setup, I transitioned it to parametrized tests as that implementation is much terser.

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 91.71%. Comparing base (be9af7f) to head (089e975).
Report is 42 commits behind head on main.

Files with missing lines	Patch %	Lines
pymatsolver/solvers.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #47      +/-   ##
==========================================
+ Coverage   89.36%   91.71%   +2.34%     
==========================================
  Files           5        7       +2     
  Lines         301      374      +73     
==========================================
+ Hits          269      343      +74     
+ Misses         32       31       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[jcapriot]

Hey @mplough-kobold i kinda hijacked your PR here! Thanks for getting this going.