KIP-863 — Reduce CompletedFetch#parseRecord() memory copy

Accepted Kafka 3.6 ClientConsumer

Adds an overloaded `Deserializer#deserialize(String, Headers, ByteBuffer)` method and updates `CompletedFetch#parseRecord()` to use `ByteBuffer` directly instead of converting to `byte[]` before deserialization. The current implementation calls `Utils.toArray(ByteBuffer)` on every record's key and value during fetch processing, causing unnecessary heap allocation and memory copy for every consumed record.

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