Fix pytest

[aewallwi]

Fix lingering issues in pytest migration that are hindering proper coverage recording and codecov checks. Verbatum translation of existing unittests into pytest compatible tests. Issues of organization of the existing tests addressed in #117.

[codecov]

Codecov Report

Merging #116 (ae90d9d) into main (e6075ad) will increase coverage by 48.80%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             main     #116       +/-   ##
===========================================
+ Coverage   38.04%   86.84%   +48.80%     
===========================================
  Files          10        7        -3     
  Lines        2363     1460      -903     
===========================================
+ Hits          899     1268      +369     
+ Misses       1464      192     -1272     

Flag	Coverage Δ
unittests	86.84% <ø> (+48.80%)	⬆️

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Impacted Files	Coverage Δ
uvtools/plot.py	72.80% <0.00%> (+72.80%)	⬆️
uvtools/version.py	79.62% <0.00%> (+79.62%)	⬆️
uvtools/dspec.py	96.41% <0.00%> (+96.41%)	⬆️
uvtools/utils.py	97.05% <0.00%> (+97.05%)	⬆️
uvtools/__init__.py	100.00% <0.00%> (+100.00%)	⬆️
uvtools/data/__init__.py	100.00% <0.00%> (+100.00%)	⬆️

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[r-pascua]

It looks like the coverage is working and that all the tests are passing. Since we're not worrying about modularizing tests in this PR, I'm happy to approve as-is. I think that now the tests for the plotting tools I wrote are kind of wonky, but I'll get to that in a future PR.

Thank you for doing this!