KIP-958 — Tiered Storage Metrics

Discussion Tiered StorageMetrics

Adds cache hit, miss, eviction, and load success/failure metrics for the `RemoteIndexCache` used in Tiered Storage to fetch remote segment index files (offset index, time index). Without cache observability metrics, operators cannot distinguish whether a performance problem during remote fetch is caused by cache thrashing versus slow remote storage, making Tiered Storage debugging difficult.

Details