[Backend] Caching: add read-through Redis cache + invalidation for trust score endpoint

[Baskarayelu]

Description

GET /api/trust/:address recomputes the full trust score on every request from the data store with no caching, while bond and attestation reads already use bondCacheService/attestationCacheService. Trust scores change only when a bond, attestation, or slash event is applied, so they are ideal for read-through caching with explicit invalidation. We should add a trust cache namespace in src/cache/redis.ts and invalidate it from the identity-state-sync path.

Requirements and context

• Add a trust namespace cache wrapper analogous to src/services/bondCacheService.ts.
• Invalidate via src/cache/invalidation.ts when src/listeners/identityStateSync.ts applies bond/attestation/slash changes.
• Record cache hit/miss and stale-read metrics using existing src/middleware/metrics.ts helpers (recordStaleCacheRead).
• TTL must be configurable through src/config/index.ts.

Suggested execution

Create branch feature/trust-score-cache.

• Add src/services/trustCacheService.ts and tests.
• Hook invalidation in src/listeners/identityStateSync.ts.
• Add metrics + config entry.
• Update docs/caching.md and docs/CACHE_INVALIDATION.md.

Test and commit

Run npm run test. Edge cases: cache miss → set, invalidation on state change, stale-read detection, Redis unavailable (fail open to DB). Security: never cache across tenants incorrectly.

Example commit message

feat: add read-through Redis cache and invalidation for trust scores

Guidelines

• Minimum 95% test coverage
• Clear documentation in docs/caching.md
• Timeframe: 96 hours

[drips-wave]

@Baskarayelu Ajibose could not be assigned to this issue because they have reached the maximum of 4 accepted assignments per organization in the current wave of the Stellar Wave Program.

The assignee has been removed. Please choose a different contributor.

[OAKVISUALZ]

Please assign me this issue.

[drips-wave]

⚠️ @Baskarayelu: @OAKVISUALZ has been assigned to this issue but hasn't applied to it via Drips Wave.

This issue is still part of the Stellar Wave Program, so Wave contributors can still apply and be assigned. If you'd rather hand it off outside of Wave, remove the Stellar Wave label to take this issue out of the Wave Program.