[genZIn4532]

Summary of Changes

Closes #2069

Adds comprehensive unit test coverage verifying EventIndexer deduplication, repeated ledger processing, and unique constraint collision behavior.

• Repeated Ledger Ingestion: Asserts that re-processing identical raw events from duplicate or replayed ledgers does not re-insert duplicate event rows and skips redundant user score updates.
• Reordered Events: Verifies out-of-order sequence tokens within a ledger batch are handled idempotently without breaking batch transactions.
• Unique Constraint Retries: Asserts that database unique constraint conflicts () gracefully succeed with and trigger zero side-effects.
• Test Suite: 13/13 unit tests passing 100% clean in .