fix: align Python version classifiers

[dcfocus]

Summary

• Remove Python 3.9 and 3.10 classifiers because requires-python is >=3.11,<3.14.
• Add the Python 3.13 classifier.
• Extend packaging metadata tests to guard supported-version classifier drift.

Closes #70

Testing

• uv lock --check
• uv run --project python --extra dev ruff format --check python/tests/test_packaging_metadata.py python/pyproject.toml
• uv run --project python --extra dev ruff check python/tests/test_packaging_metadata.py
• uv run --project python --extra tests pytest python/tests/test_packaging_metadata.py -q
• cd python && uv run --extra dev pyright
• git diff --check