Testing/pixi in testing + Python 3.14 basic support

[jlnav]

Trying this again - this will also make it easier to chase down CI bugs

December update: Adjusted to only perform basic tests (for now). Future PR can incrementally add deps/tests for extra tests.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.29%. Comparing base (229f7f9) to head (e350ad6).
⚠️ Report is 3 commits behind head on develop.

❗ There is a different number of reports uploaded between BASE (229f7f9) and HEAD (e350ad6). Click for more details.

HEAD has 9 uploads less than BASE

Flag	BASE (229f7f9)	HEAD (e350ad6)
	21	12

Additional details and impacted files

@@             Coverage Diff              @@
##           develop    #1609       +/-   ##
============================================
- Coverage    93.33%   78.29%   -15.04%     
============================================
  Files           76       76               
  Lines         7580     7580               
  Branches      1119     1119               
============================================
- Hits          7075     5935     -1140     
- Misses         330     1460     +1130     
- Partials       175      185       +10     

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