MAINT switch CI to use pixi

[glemaitre]

Wide maintenance PR:

• move from Azure to GitHub Action
• Use pixi to lock packages
• Create a bot to update the packages
• Endorse SPEC0

[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 2 lines in your changes missing coverage. Please review.

Project coverage is 86.39%. Comparing base (980cc94) to head (cddaac4).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
imblearn/datasets/_zenodo.py	50.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1098      +/-   ##
==========================================
- Coverage   92.98%   86.39%   -6.60%     
==========================================
  Files         105       58      -47     
  Lines        8323     4291    -4032     
  Branches     1288      853     -435     
==========================================
- Hits         7739     3707    -4032     
- Misses        465      472       +7     
+ Partials      119      112       -7     

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