Update CI/CD to use pixi and parallel testing; also moving to Python 3.11-3.13

[timtreis]

No description provided.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.08%. Comparing base (c60c29d) to head (81712c2).
⚠️ Report is 35 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #481      +/-   ##
==========================================
+ Coverage   83.95%   84.08%   +0.12%     
==========================================
  Files           8        8              
  Lines        1839     1841       +2     
==========================================
+ Hits         1544     1548       +4     
+ Misses        295      293       -2     

Files with missing lines	Coverage Δ
src/spatialdata_plot/pl/utils.py	78.37% <100.00%> (+0.22%)	⬆️

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[Copilot]

Pull Request Overview

This PR refactors random number generation across the test suite by centralizing it through a standardized function and removes unused RNG variables. It also adds a warning when a specified table doesn't annotate the target element and includes various development environment improvements.

• Replaced direct RNG instantiation with centralized get_standard_RNG() function for consistent test reproducibility
• Added warning validation when table_name and color are specified but the table doesn't annotate the element
• Updated development tooling with pixi configuration and GitHub Actions improvements

Reviewed Changes

Copilot reviewed 12 out of 20 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/conftest.py	Replaced global RNG with get_standard_RNG() function to ensure consistent random state initialization
tests/pl/test_*.py	Updated all test files to use centralized RNG function and removed unused RNG variables
src/spatialdata_plot/pl/utils.py	Added warning when specified table doesn't annotate element and simplified assignment syntax
pyproject.toml	Updated development dependencies and added pixi workspace configuration
.github/workflows/test.yaml	Migrated to pixi-based testing environment with improved caching

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