[Test] Add unit tests for RequestBuilder request-code mapping and header field propagation

Description

remoting/src/main/java/org/apache/rocketmq/remoting/rpc/RequestBuilder.java has no direct unit test coverage. The class contains non-trivial public static behavior used to build RPC requests across the codebase:

• request-code-to-header-class lookup (PullMessageRequestHeader, GetConsumerListByGroupRequestBody, CloneGroupOffsetRequestHeader, QueryConsumerOffsetRequestHeader, UpdateConsumerOffsetRequestHeader),
• reflection-based header construction,
• oneway/brokerName/topic/queueId/lo field propagation across several overloads (including nullable Boolean queueId handling),
• the unknown-request-code rejection branch (UnsupportedOperationException).

remoting/src/test/java/org/apache/rocketmq/remoting/rpc/ contains tests for ClientMetadata, RpcClientImpl and RpcRequestHeader, but no test references RequestBuilder anywhere in the repo's test sources. A regression in the request-code mapping or in field propagation would currently go unnoticed.

Expected behavior

Add a focused RequestBuilderTest that pins the current contract: each supported request code returns the expected header type with all fields propagated, and unknown request codes fail with UnsupportedOperationException mentioning the code.