Prepare Python package metadata for Determa State 0.2.0

[fruwe]

Closes #80

Summary

• Set the Python package and authoritative release metadata to 0.2.0.
• Pin specification v0.2.0 at 7782671b56165a59caa61a65c29fefc63105ebf8.
• Pin conformance v0.2.0 at d6a45d31614ee25de20476ed93f10e14997d882c.
• Confirm the bundled schemas already match the pinned specification and document the established 0.2.0 release scope.
• Preserve engine and adapter behavior.

Validation

• Python 3.11: ruff, mypy, 274 unit tests, 288 pinned conformance tests
• Python 3.13: ruff, mypy, 274 unit tests, 288 pinned conformance tests
• PostgreSQL 16: 5 adapter tests
• Built determa_state-0.2.0 wheel and sdist
• twine check
• Distribution metadata, packaged schemas and pins, release tag verification, and duplicate archive-member protection
• git diff --check

Release Boundary

A v0.2.0 tag triggers PyPI Trusted Publishing after manual pypi environment approval. This PR does not create a tag, publish a package, approve that environment, or merge the release.