Use pixi to simplify ci jobs

[maxrjones]

Uses pixi in the non-zarr CI jobs as well, to simplify the setup

TODO:

• Unit tests and/or doctests in docstrings
• Tests pass locally
• Docstrings and API docs for any new/modified user-facing classes and functions
• Changes documented in docs/release.rst
• Docs build locally
• GitHub Actions CI passes
• Test coverage to 100% (Codecov passes)

[maxrjones]

I need to do more work on this PR before it's ready, switching it to draft now

[d-v-b]

sounds good! I trust you to merge this when everything is green

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.33%. Comparing base (eab1742) to head (857feb8).

❌ Your project status has failed because the head coverage (99.33%) is below the target coverage (100.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #825   +/-   ##
=======================================
  Coverage   99.33%   99.33%           
=======================================
  Files          26       26           
  Lines         898      898           
=======================================
  Hits          892      892           
  Misses          6        6           

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[maxrjones]

This turned out to be hard for me to fix, so I decided a complete modernization was warranted. So this is superseded by #826, which removes the need for pixi usage.