Try general python test workflow

[jeromekelleher]

This refactors the main tests computing coverage to use the general workflow. Turns out a lot of the complexity isn't needed any more with the uv setup (yay for uv!).

The odds and ends that don't fit in elsewhere are included as bespoke python tests.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.10%. Comparing base (e579e13) to head (1382d37).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3398      +/-   ##
==========================================
+ Coverage   92.32%   94.10%   +1.77%     
==========================================
  Files          45       48       +3     
  Lines       43605    51206    +7601     
  Branches     5716     5716              
==========================================
+ Hits        40259    48187    +7928     
- Misses       1904     2593     +689     
+ Partials     1442      426    -1016     

Flag	Coverage Δ
C	91.33% <ø> (ø)
c-python	76.94% <ø> (?)
python-tests	96.56% <ø> (ø)
python-tests-no-jit	33.42% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
Python API	98.88% <ø> (ø)
Python C interface	91.20% <ø> (∅)
C library	93.56% <ø> (+2.23%)	⬆️

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