[kafka] Integrate Produce with native Fluss append

[gyang94]

Purpose

Part of #4185. PR07 of the Kafka compatibility sequence.

Wire the Produce handler and raw/string transcoder to the TabletServer append gateway. Apply the same table admission contract as Metadata, isolate conversion and append errors per partition, map acknowledgements and offsets, and register Produce v3-v11.

Acceptance criteria

• Only compatible pre-created tables and valid bucket IDs reach append.
• One invalid table or partition does not suppress independent valid writes.
• Gateway acks/timeout and partition offsets/replication errors map correctly.
• Kafka calls tryCompleteActions immediately after synchronous produceLog invocation, including throws, without waiting for async acknowledgements.
• A real Kafka producer discovers native DDL tables and writes raw/string records with acks=0/1/all; native Fluss readback verifies data and metadata.

Dependencies

PR06 raw/string conversion (#4282) and independent core PR #3412 / #3455. Core changes remain owned by #3412.

Scope boundary

No new core implementation, Kafka table creation, JSON, authentication, idempotence or transactions.

Implementation

Draft PR #4286: #4286

Java 11 validation: 82 unit tests and 4 integration tests passed at dc5fb6599b8c5e155cb17280df71a74ee34c9ffa. Review and merge remain pending.