feat: drop support for Python <=3.10 and require >=3.11

[kgala2]

Drop support for Python 3.9 and 3.10 as both have reached upstream End of Life (EOL). Minimum required Python version is now >=3.11.

Summary of Changes:

• Bump requires-python in pyproject.toml to >=3.11
• Remove Python 3.9 and 3.10 from pyproject.toml classifiers and add 3.14
• Bump [tool.mypy] python_version to 3.11
• Update TEST_PYTHON_VERSIONS in noxfile.py to ["3.11", "3.12", "3.13", "3.14"]
• Update .github/workflows/tests.yml matrix from 3.10 to 3.11
• Apply Ruff code modernization for Python 3.11+ (UP035 collections.abc.Callable, UP017 datetime.UTC)

Verification:

• ./build.sh lint: Passed (Ruff, Mypy, Twine check)
• ./build.sh test: 200/200 unit tests passed

[kgala2]

/gcbrun