test: add unit coverage for retry, provenance, pool, and notification templates

[Davidemulo]

Summary

• Add unit tests for retry policy backoff, max retry normalization, jitter, failure classification, and metrics
• Add provenance service tests for available lineage records, filtered graph queries, and traversal from sources to destinations
• Add pool service tests for multi-AMM aggregation, pair filtering, comparisons, depth metrics, and large liquidity events
• Add notification template tests for rendering, variable validation, channel/status variants, and approval/update flows

Tests

• npm run test:unit --workspace=backend -- retryPolicy.service.test.ts provenance.service.test.ts pool.service.test.ts notificationTemplate.service.test.ts
• Attempted npm run test:backend; stopped after several minutes due unrelated existing Redis connection refusals/timeouts and unrelated suite failures

Closes #706
Closes #707
Closes #708
Closes #709

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