PR: Add backend for Pixi

[ccordoba12]

Pixi is not only quite fast, it also has much better support to export/import environments.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 62.78317% with 115 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.76%. Comparing base (6065082) to head (39f3054).
⚠️ Report is 26 commits behind head on main.

Files with missing lines	Patch %	Lines
envs_manager/backends/pixi_interface.py	56.43%	99 Missing and 16 partials ⚠️

❗ There is a different number of reports uploaded between BASE (6065082) and HEAD (39f3054). Click for more details.

HEAD has 6 uploads less than BASE

Flag	BASE (6065082)	HEAD (39f3054)
	12	6

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #33      +/-   ##
==========================================
- Coverage   80.73%   73.76%   -6.98%     
==========================================
  Files           8        9       +1     
  Lines         758     1052     +294     
  Branches       87      118      +31     
==========================================
+ Hits          612      776     +164     
- Misses        107      219     +112     
- Partials       39       57      +18     

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