feat: Implement centralized cache invalidation service

[softnationz]

closes #457

This PR implements a centralized cache invalidation service to prevent stale reads in the BOXMEOUT platform. The service provides a clean API for cache operations with automatic invalidation when underlying data changes.

Changes

Core Service Enhancements (cache.service.ts)

• ✅ Added get<T>(key) - Type-safe cache retrieval
• ✅ Added set(key, value, ttl) - Cache storage with TTL
• ✅ Added del(key) - Single key deletion
• ✅ Added delPattern(pattern) - Pattern-based bulk invalidation using Redis SCAN
• ✅ Added getOrSet<T>(key, ttl, compute) - Read-through caching pattern
• ✅ Maintained backward compatibility with legacy API (cacheGet, cacheSet, etc.)

Cache Key Namespaces

Implemented consistent namespacing for organized cache management:

• market:{id} - Individual market data
• market:{id}:stats - Market statistics
• markets:* - Market list queries
• leaderboard:global:* - Global leaderboard data
• user:{id}:balance - User balance data
• platform:stats - Platform-wide statistics

MarketService Integration

• Updated all cache operations to use new API
• Added proper cache invalidation after write operations
• Implemented invalidateMarketCache() for comprehensive market cache clearing
• Applied invalidation in bulkPauseMarkets() and bulkCancelMarkets()

Testing

• ✅ 23 comprehensive unit tests covering:
  • Basic CRUD operations (get, set, del)
  • Pattern-based invalidation with Redis SCAN
  • getOrSet read-through caching
  • Error handling and graceful degradation
  • Namespaced key operations
  • Cache invalidation workflows
  • Legacy API compatibility

Documentation

• Created comprehensive CACHE_SERVICE_README.md with:
  • API reference and usage examples
  • Cache key namespace conventions
  • Invalidation strategies and best practices
  • Integration examples for services
  • Performance considerations
  • Migration guide from legacy API

Acceptance Criteria

• cache.service.ts exposes: get, set, del, delPattern, getOrSet
• delPattern('market:*') purges all market cache entries using Redis SCAN
• Cache keys namespaced: market:{id}, leaderboard:global:*, user:{id}:balance
• After any write in market.service.ts, relevant cache keys are invalidated
• Unit test: set → get → invalidate → get returns null ✅ (23 tests passing)