[kafka] Add request and transport framework #4264

Parent issue

Part of #4185 — Kafka Protocols Compatibility: Basic Produce.

Motivation

Provide the reusable request and transport foundation for small, independently reviewable Kafka API implementations. This issue establishes the infrastructure; it does not implement a new concrete API handler.

Scope

• Add request context, API specifications, typed handlers, a capability registry, asynchronous dispatch, and common error mapping.
• Propagate listener and connection context from the Kafka transport.
• Handle request/response buffer ownership, including idempotent release and cleanup on serialization failure.
• Recognize configured Kafka protocol endpoints in the Netty server.
• Retain the existing request-handler behavior until the ApiVersions follow-up connects the dispatcher to production.

Acceptance criteria

• Registry and dispatcher tests cover registration, version checks, asynchronous completion, and handler failures.
• Request context reaches handlers without losing listener or connection information.
• Request and response buffers are released correctly on successful and failing paths.
• Relevant Kafka and RPC unit/integration tests, formatting, and license checks pass.
• The focused implementation is reviewed and merged before dependent stages are completed.

Out of scope

Concrete ApiVersions/Metadata handlers, Produce, authentication, schema conversion, Kafka CreateTopics/DeleteTopics, and automatic table creation.

Implementation and review

Implementation PR: #4259.

This is the first foundation stage. The ApiVersions and Metadata issues build on it. Track completion in this issue rather than in a PR checklist on the umbrella.