Added In-Memory Cache for Faster Skipping Index Queries

Added an in-memory cache for deserialized skipping index granules. This should make repeated queries that use skipping indexes faster. The size of the new cache is controlled by server settings skipping_index_cache_size and skipping_index_cache_max_entries. The original motivation for the cache were vector similarity indexes which became a lot faster now. #70102 (Robert Schulze).