Trie-based memtable implementation replaces skiplist memtables

Cassandra 5.0 introduces trie-based memtables as the new default implementation, replacing the previous skiplist-based memtables. This changes memory layout and access patterns, potentially affecting memtable flush behavior and read latencies.

Monitor cassandra_memtable_live_data_size and cassandra_memtable_switch metrics for changes in memtable behavior patterns. Baseline read latencies (cassandra_client_request_read_time_50p) after upgrade. Review memtable configuration parameters for trie-specific tuning options.