Support Send Batch Msg Synchronously

**Is your feature request related to a problem? Please describe.**
Currently, if you send message synchronously, only a message can be send. how about support a way send batch messages synchronously

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The issue names no files, tests, or entry points. Start by locating the synchronous message-send API and the existing batch-message path, then define how synchronous batch sending should behave and verify that the client can send multiple messages through it.

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