KIP-596 — Safely abort Producer transactions during application shutdown

Discussion TransactionsProducer

Adds a `close(Duration timeout)` overload to `KafkaProducer` that automatically calls `abortTransaction()` when the producer is in a non-recoverable error state before closing, instead of requiring users to manually invoke `abortTransaction` inside a nested try-catch. The existing error handling pattern for transactional producers is complex because `abortTransaction()` itself can throw if the producer is already fenced or in a fatal state.

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