ci: Add multi python version configuration for testing

[lsetiawan]

This pull request includes several updates to the CI configuration and environment setup for the phylo2vec project. The main changes involve adding support for multiple Python environments and restructuring the environment definitions in the pixi.toml file.

CI Configuration Updates:

• .github/workflows/ci-python.yml: Updated the CI workflow to support multiple Python environments (py310, py311, py312) and removed the hardcoded PIXI_PYTHON_ENV variable.

Environment Definitions:

• pixi.toml:
  • Added new environment definitions for py310, py311, and py312.
  • Restructured the py-phylo2vec and r-phylo2vec environments to include features and solve groups.
  • Updated feature dependencies to specify Python versions (3.10.*, 3.11.*, 3.12.*) and added new features for pydev and pydocs.

Dependency Updates:

• py-phylo2vec/pyproject.toml: Added six as a dependency, which is required by ete3.

Related Issues

Closes #90

[deepsource-io]

Here's the code health analysis summary for commits 879d014..b188319. View details on DeepSource ↗.

Analysis Summary

Analyzer	Status	Summary	Link
Rust	✅ Success		View Check ↗
Python	✅ Success		View Check ↗

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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