Fix Pixi platform setup in package CI

[AndrewSazonov]

Summary

• configure CI-created Pixi projects with runner-specific rich platform entries
• avoid solving unqualified macOS/Linux PyPI targets that can fall back to source builds
• format non-Python documentation files with the Prettier version installed by CI

Verification

• pixi run nonpy-format-check
• git diff --check
• pixi run check
• pixi run docs-build

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.34%. Comparing base (883c384) to head (4b80a3b).
⚠️ Report is 123 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #216      +/-   ##
===========================================
+ Coverage    82.26%   90.34%   +8.08%     
===========================================
  Files           88      284     +196     
  Lines         5451    24664   +19213     
  Branches       454     2897    +2443     
===========================================
+ Hits          4484    22282   +17798     
- Misses         802     1756     +954     
- Partials       165      626     +461     

Flag	Coverage Δ
integration	?
unittests	90.34% <ø> (+17.89%)	⬆️

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see 329 files with indirect coverage changes

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