Ci setup

[pacrob]

This PR introduces several infrastructure and compatibility updates:

• Dropped Python 3.9 support across docs, examples, and metadata.
• Added tox.yml workflow with a full Python/tox matrix (3.10–3.13).
• Added .readthedocs.yaml with pinned Python version and fail_on_warning.
• Unified lint to run pre-commit instead of direct ruff.
• Split docs into docs and docs-ci with -W warnings enabled.