Pixi package migration

[mpatrou]

Short description of the changes:

The changes include migrating from conda package/environment to pixi.
Big part of this work follows: Migrate to Pixi #174, Quicknxs - Fix package version number set by hatch build #180 and python_project_template

Long description of the changes:

• pixi package/environment migration
• github actions for pixi, conda-verify, renaming for consistency etc.
• readthedocs
• pylint warning fixed
• move to a later pyoncat version
• documentation, readme instructions for pixi

Check list for the pull request

• I have read the [CONTRIBUTING]
• I have read the [CODE_OF_CONDUCT]
• I have added tests for my changes
• I have updated the documentation accordingly

Check list for the reviewer

• I have read the [CONTRIBUTING]
• I have verified the proposed changes
• best software practices
  • all internal functions have an underbar, as is python standard
  • clearly named variables (better to be verbose in variable names)
  • code comments explaining the intent of code blocks
• All the tests are passing
• The documentation is up to date
• code comments added when explaining intent

Manual test for the reviewer

References

EWM: Migrate Build (CI) from Conda to PIXI

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 83.76%. Comparing base (1878c65) to head (c584283).

Files with missing lines	Patch %	Lines
src/shiver/views/histogram_parameters.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             next     #168   +/-   ##
=======================================
  Coverage   83.76%   83.76%           
=======================================
  Files          42       42           
  Lines        6626     6626           
=======================================
  Hits         5550     5550           
  Misses       1076     1076           

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