move tests to micromamba and update gh-actions versions

[callumrollo]

The tests here will fail as they default to numpy 2. Need to either refactor np.NaN >> np.nan or merge #183 first

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.50%. Comparing base (eff60ad) to head (179b508).
Report is 55 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #184       +/-   ##
===========================================
- Coverage   80.32%   56.50%   -23.83%     
===========================================
  Files           7        9        +2     
  Lines        1357     1646      +289     
===========================================
- Hits         1090      930      -160     
- Misses        267      716      +449     

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[callumrollo]

I think codecov has been silently broken for a while. This PR would bring it back into service

[jklymak]

Thanks @callumrollo