• [Feature] Add FD-based polling mode (config.polling.mode = :fd) as an alternative to the default thread-based polling. FD mode uses a single Ruby thread with IO.select for efficient multiplexing, providing 39-54% higher throughput, lower memory usage, and fewer threads compared to the default thread mode.
• [Feature] Add config.polling.fd.max_time setting (default: 100ms) to control maximum polling time per producer per cycle. This enables per-producer priority differentiation.
• [Feature] Add Producer#queue_size (alias: #queue_length) to return the count of messages pending in the librdkafka queue. This counts messages that have been dispatched to librdkafka but not yet transmitted to the Kafka broker.
• [Enhancement] Add poll_nb and poll_drain methods to rdkafka Producer for efficient non-blocking polling without GVL release overhead.
• [Enhancement] Add poller.producer_registered and poller.producer_unregistered instrumentation events for FD mode.
• [Change] Update to use max_wait_timeout_ms parameter in rdkafka AbstractHandle#wait for consistency with librdkafka conventions.
• [Change] Require karafka-rdkafka >= 0.24.0 due to max_wait_timeout_ms API change and FD polling support.