Fix: Add mutex lock for state completion check in gRPC streaming to prevent race condition

[pskiran1]

What does the PR do?

This PR aims to fix an occasional error (caused by a race condition) that occurs when making multiple asynchronous requests to the ASR model in decoupled mode:

E0829 13:41:44.609857 147 stream_infer_handler.cc:528] "Should not print this! Decoupled should NOT write via WRITEREADY!"

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Test plan:

• CI Pipeline ID: 18428769

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Background

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• closes GitHub issue: #xxx

[indrajit96]

LGTM