KIP-691 — Enhance Transactional Producer Exception Handling

Accepted TransactionsProducer

Adds a `fencedOnCommit` classification to transactional producer exceptions to distinguish fatal epoch-fenced errors (where the producer must abort and re-initialize) from transient errors (where only an `abortTransaction()` is needed). Previously, all `ProducerFencedException` and `OutOfOrderSequenceException` types required full `initTransactions()` restarts, causing unnecessary downtime for recoverable faults.

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