• [Enhancement] Introduce reload_on_idempotent_fatal_error to automatically reload librdkafka producer after fatal errors on idempotent (non-transactional) producers.
• [Enhancement] Add configurable backoff and retry limits for fatal error recovery to prevent infinite reload loops:
  • wait_backoff_on_idempotent_fatal_error (default: 5000ms) - backoff before retrying after idempotent fatal error reload
  • max_attempts_on_idempotent_fatal_error (default: 5) - max reload attempts for idempotent fatal errors
  • wait_backoff_on_transaction_fatal_error (default: 1000ms) - backoff after transactional fatal error reload
  • max_attempts_on_transaction_fatal_error (default: 10) - max reload attempts for transactional fatal errors
• [Enhancement] Ensure error.occurred is instrumented before idempotent fatal error reload for visibility.
• [Enhancement] Automatically reset fatal error reload attempts counter on successful produce/transaction to allow recovery.
• [Refactor] Extract idempotence-related logic into separate WaterDrop::Producer::Idempotence module.
• [Refactor] Initialize @idempotent and @transactional instance variables in Producer#initialize for consistent Ruby object shapes optimization.
• [Refactor] Add idempotent_reloadable? and idempotent_retryable? methods to encapsulate idempotent fatal error reload checks.
• [Refactor] Add transactional_retryable? method to encapsulate transactional fatal error reload retry checks.
• [Fix] Waterdrop config.kafka errors on frozen hash.
• [Fix] Producer#transactional? method now correctly computes transactional status when @transactional is initialized to nil.