• [Fix] Fatal error replacement not working without exact error unwind from the fatal envelope
• [Testing] Add WaterDrop::Producer::Testing module for injecting and querying librdkafka fatal errors in tests.
• [Testing] Add #trigger_test_fatal_error(error_code, reason) method to simulate fatal errors without requiring actual broker-side conditions.
• [Testing] Add #fatal_error method to query current fatal error state for validation in tests.
• [Testing] Add comprehensive test coverage for fatal error injection, reload behavior, and event instrumentation with real librdkafka errors.
• [Change] Require karafka-rdkafka >= 0.23.1 due to error handling fixes.