- 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
- Add Cost field to Edge and RouteLeg structs
- Propagate Cost in FindRoute itinerary creation
- Write TestRouteParetoRanking test verifying non-dominated route selection
