[kafka] Transcode mapped raw and string records to Arrow

[gyang94]

Purpose

Part of #4185. PR06 of the Kafka compatibility sequence.

Use the DDL mapping contract to decode raw/string keys and values, assemble physical rows with optional timestamps and ordered headers, and encode owned native Arrow log bytes.

Acceptance criteria

• Raw bytes and strict UTF-8 strings map to the configured physical columns.
• Nullable values, empty bytes, NOT NULL violations and duplicate/nullable headers are handled correctly.
• The native batch uses the table schema ID and remains readable after Arrow resources close.
• Arrow writers and allocators close on encoding failures.

Dependencies

PR05 Produce protocol (#4281); reuses the PR03 DDL contract (#4277 / #4275).

Scope boundary

No JSON decoding, gateway append, protocol registration or core module changes.

Implementation

Draft PR #4285: #4285

Java 11 validation: 75 unit tests and 2 integration tests passed at 503136295d6bbaed81b7e7845dceb2d64db2d9d4. Review and merge remain pending.