Fix Py-API checks with newer maturin and mypy

[chrjabs]

Description of the Contribution

Fixes failing checks in #216 (and includes it), as well as another small issue with the newest maturin.

• fix(pyapi): stricter pyproject.toml requirements
• fix(pyapi): specify __all__ in python stubs
• chore(deps): update install-pinned/mypy digest to 75779f1

PR Checklist

• I read and agree to CONTRIBUTING.md
• I have formatted my code with rustfmt / cargo fmt --all
• Commits are named following conventional commits
• I have added documentation for new features
• The test suite still passes on this PR
• I have added tests for new features / tests that would have caught the bug this PR fixes (please explain if not)
• If this PR contains breaking changes, it is against the next-major branch, not against main