M2 #25: Redis integration: Caching and pub/sub

[joaquinbejar]

Summary

Implements Redis integration for caching frequently accessed data and pub/sub messaging between services. This improves API response times and enables real-time communication.

Changes

New Module: indexer/src/cache/

File	Description
mod.rs	Module exports
config.rs	RedisConfig with connection and TTL settings
store.rs	RedisCache for caching operations
pubsub.rs	RedisPubSub for real-time messaging
metrics.rs	CacheMetrics for monitoring

Caching Layer

• Market metadata (TTL: 1 minute)
• Order book snapshots (TTL: 1 second)
• Recent trades (TTL: 10 seconds)
• User balances (TTL: 5 seconds)

Cache Operations

• get/set/delete with TTL support
• Type-safe serialization via serde
• Convenience methods: get_market, set_orderbook, get_trades, etc.
• Cache invalidation: invalidate_market, invalidate_user

Pub/Sub Channels

• book:{market} — Book update notifications
• trades:{market} — Trade notifications
• orders:{owner} — User order updates

Graceful Degradation

• Configurable enabled/disabled state
• Available/unavailable tracking
• No-op when disabled or unavailable

CacheMetrics Tracking

• Hits/misses/errors
• Gets/sets/deletes/publishes
• Hit rate and ops/sec
• Snapshot for monitoring

Dependencies

• Add redis (v0.29) with tokio-comp and connection-manager features
• Add deadpool-redis (v0.21) for connection pooling

Technical Decisions

• Placeholder implementation: Real Redis operations are stubbed; actual implementation will use redis-rs commands
• Cache-aside pattern: Get from cache, if miss then fetch from source and populate cache
• Graceful degradation: Service continues to work if Redis is unavailable
• Shared metrics: Metrics can be shared across cache and pubsub instances

Testing

• 50+ unit tests for all components
• RedisConfig validation tests
• RedisCache operations tests (get, set, delete)
• RedisPubSub publish tests
• CacheMetrics recording and hit rate tests
• Graceful degradation tests (disabled/unavailable)

Checklist

• Code follows .internalDoc/09-rust-guidelines.md
• Documentation added for all public items
• No warnings from cargo clippy
• cargo fmt passes
• All tests pass

Closes #25