Record model build provenance in release manifests

[MaxGhenis]

Summary

• add build ids, timestamps, and build-time model metadata to UK release manifests
• populate release-manifest uploads from policyengine_uk build metadata
• extend release manifest tests to cover the new provenance fields

Testing

• uv run pytest policyengine_uk_data/tests/test_release_manifest.py
• uv run ruff check policyengine_uk_data/utils/release_manifest.py policyengine_uk_data/utils/data_upload.py policyengine_uk_data/tests/test_release_manifest.py
• python3 -m py_compile policyengine_uk_data/utils/release_manifest.py policyengine_uk_data/utils/data_upload.py policyengine_uk_data/tests/test_release_manifest.py