Fix Stage 12 comparison and UK geography metadata

[anth-volk]

Fixes #701

Summary

This PR makes Stage 12 result comparison ignore numeric differences of 0.01 or less and requires complete UK geography metadata before a child simulation reports success.

Changes

• Compare numeric leaves with decimal arithmetic and an inclusive absolute tolerance of 0.01 while retaining exact artifact digests.
• Resolve constituency and local-authority names and coordinates from the two canonical PolicyEngine UK lookup files.
• Fail explicitly when lookup files, result records, names, or coordinates are unavailable.
• Validate that the Stage 12 service credentials can read the required lookup objects.
• Document the lookup dependency and its restricted GCS permissions.
• Add unit tests for the exact 0.01 comparison boundary, UK geography resolution, and deployment validation.

Testing

• Executor test suite: 611 passed, 24 skipped, and 2 deselected.
• Focused comparison tests: 6 passed.
• Black and Ruff checks for the changed comparison modules: passed.
• git diff --check: passed.

Deployment notes

The staging and production Stage 12 service accounts already have conditional read access to only the two required lookup objects. Activating the runtime changes requires a Stage 12 Modal deployment; this PR does not redirect user traffic.