Add macOS and Windows CI coverage for Python 3.10-3.12

[laynepenney]

Finding

The package declares support for Python 3.10, 3.11, and 3.12 and is intended as a cross-platform adoption surface, but CI currently verifies only Ubuntu.

Current .github/workflows/ci.yml:

• lint: ubuntu-latest, Python 3.12
• test matrix: ubuntu-latest, Python 3.10 / 3.11 / 3.12

No macOS or Windows jobs are present.

Validation performed manually

Source checkout: b312868.

• macOS local, Python 3.11.9: source install, 226 tests, all 3 examples passed
• Linux Docker, Python 3.10.20: source install, 226 tests, all 3 examples passed
• Linux Docker, Python 3.11.15: source install, 226 tests, all 3 examples passed
• Linux Docker, Python 3.12.13: source install, 226 tests, all 3 examples passed

Gap

Windows was not locally verified. macOS was verified only on Python 3.11 because local pyenv has 3.11.9 and 3.13.2 installed, not 3.10/3.12.

Recommendation

Add a CI job for release/adoption readiness across:

• ubuntu-latest, macos-latest, windows-latest
• Python 3.10, 3.11, 3.12
• source install plus pytest -q
• optionally run the three examples as smoke tests

This turns the current manual validation into a durable gate.