- Remove Python 3.8 and 3.9 from the test workflow matrix, keeping only 3.10, 3.11, and 3.12
- Update pyproject.toml version from 1.15.0 to 1.16.0 and relax requires-python from >=3.12 to >=3.10
- Add CHANGELOG entry for version 1.16.0 documenting the release and internal cleanup
