This protocol is used to build Fetch requests.

Implementations must populate the request struct with:

• replica_id - Should be -1 for consumers
• max_wait_time - Maximum time to wait for messages in ms
• min_bytes - Minimum bytes to accumulate before returning
• topics - List of topic/partition/offset data to fetch
• max_bytes (V3+) - Maximum bytes to return
• isolation_level (V4+) - 0 for READ_UNCOMMITTED, 1 for READ_COMMITTED
• log_start_offset (V5+) - Log start offset for partitions
• session_id, epoch (V7+) - For incremental fetch sessions
• current_leader_epoch (V9+) - Epoch of the current leader for partitions
• rack_id (V11+) - Consumer rack ID for rack-aware fetch

All known versions (V0-V11) have explicit implementations. The Any fallback handles unknown future versions.