[codex] Expose client remote address in connect intercept

[HTHou]

Summary

Expose the connecting client Netty Channel through InterceptConnectMessage; remote socket address helpers continue to be available and now derive from the channel when no explicit address is provided.

Changes

• Thread the Netty channel from MQTTConnection through PostOffice and BrokerInterceptor.
• Add getChannel(), getRemoteAddress(), getClientAddress(), and getClientPort() to InterceptConnectMessage.
• Keep existing connect-message constructors and one/two-argument interceptor notification paths compatible.
• Add coverage proving connect intercept messages include the channel and can derive the remote address from it.

Validation

• ./mvnw -pl broker -Dtest=BrokerInterceptorTest test
• Earlier full run: ./mvnw -pl broker test -DskipITs reached Tests run: 341, Failures: 0, Errors: 0, Skipped: 6 before the local forked process hit unable to create native thread, so the full run did not complete in this environment.