- Fix type mismatch in search_cache.go: SearchWithCache now returns *yandex.Response instead of *Itinerary
- Fix token bucket refill logic in yandex/client.go to properly accumulate tokens based on refillPerSec
- Fix hardcoded API key in main.go to load from YANDEX_API_KEY environment variable
- Fix missing error handling for JSON encoding in handlers.go RouteGeoJSON function
- Fix incorrect redis.Nil handling in cache/store.go CacheAside.Exists method
- Fix incorrect error return type in station_status.go updateStationStatus to return newStatus instead of empty string
- Add metrics package tracking cache hit-rate, API quota, circuit breaker trips, search time
- Integrate metrics with cache layer, yandex client, and API handlers
- Add /metrics HTTP endpoint for Prometheus-compatible metrics exposure
- Write tests for metrics functionality across cache, yandex, and API handlers
- Update test files to support new metrics infrastructure
