Add entity evaluation checkpoint to the database

[JAORMX]

Summary

This adds the checkpoint as a JSONB structure in the database. This has
been indexed using a GIN index for efficient JSON lookups once we
hook this up to the application.

Change Type

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• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

Testing

Outline how the changes were tested, including steps to reproduce and any relevant configurations.
Attach screenshots if helpful.

Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[coveralls]

coverage: 54.34%. remained the same
when pulling 20a408d on checkpoint-db
into 84efc7e on main.