chore: drop Python 3.9, add 3.12/3.13/3.14 classifiers and CI support

[shenxianpeng]

Drop Python 3.9 (EOL at 2025-10-31) support and bump minimum to 3.10. Add missing 3.12 and 3.13 classifiers, plus 3.14 support.

• pyproject.toml: requires-python bumped from >=3.9 to >=3.10; removed 3.9 classifier; added 3.12, 3.13, 3.14 classifiers
• .github/workflows/tox.yml: replaced 3.9 with 3.14 in the lint matrix
• ruff.toml: target-version bumped from py39 to py310; applied pyupgrade fixes across 8 source files (PEP 604 union syntax, etc.)

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Assisted by Pi + DeepSeek v4

[philpep]

Please also update target-version in ruff.toml, I guess some syntax modernization is required then.

Also I guess you use AI (or even you might be an agent?), in all cases be honnest and transparent about this please (in commit message or PR description)

Thanks

[shenxianpeng]

Sure, I've updated the target-version in ruff.toml and also updated the PR description to include details about the AI tools I used.

[philpep]

I think patch 3 should be squashed in patch 2 since it's a direct consequence of it.

Otherwise full changes LGTM

[shenxianpeng]

Not sure if suqash merge is acceptable for this project. Anyway, I have squashed into 2 commits

[philpep]

Merged, thanks!

[philpep]

Not sure if suqash merge is acceptable for this project. Anyway, I have squashed into 2 commits

Could be but two commits here looks better.