Quicksilver v2: evolution of a globally distributed key-value store (Part 1)

Introduced Quicksilver v1.5, a proxy-replica architecture to reduce disk space by caching hot keys on disk (RocksDB) instead of replicating the full dataset everywhere. Implemented persistent caching with RocksDB compaction filters and LRU-like tracking for evictions. Addressed consistency challenges with asynchronous replication by introducing MVCC to maintain sequential consistency, storing historical versions of keys with replication indices.