ci: support Python 3.11 through 3.14

[gouyt13]

Summary

• raise the Python package minimum from 3.9 to 3.11
• publish Linux x86-64 wheels for CPython 3.11 through 3.14
• test the oldest and newest supported Python versions in regular CI
• build one CPython 3.11 smoke-test wheel on pull requests
• continue building all four wheels for tag releases
• update README, documentation, and Ruff's target version

Verification

• Ruff 0.16.1 formatting and lint checks passed
• built a CPython 3.14 wheel with native optimization disabled
• installed that wheel and ran the Python suite: 58 passed

Repository setting follow-up

After this PR's checks are available, update main branch protection to stop requiring Python 3.9 and Python 3.12, and require Python 3.14 instead.