Attempt to fix flaky GrpcLoggingServiceTest

[scwhittle]

Don't use future completion to validate streams were closed, instead use the existing latch.
This allows us to await on the futures that we do create to ensure that requests were sent from client. There were previous issues where not joining submitted futures could lead to them never running, not sure if that is the case here.

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[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on enhancing the stability and reliability of the GrpcLoggingServiceTest suite. The primary goal is to eliminate intermittent test failures by refining the asynchronous interaction patterns between gRPC clients and the logging service. By explicitly managing stream completion and client operation execution through CountDownLatch and future awaiting, the tests now have more robust synchronization, preventing race conditions that previously led to flakiness.

Highlights

• Test Reliability Improvement: Refactored the GrpcLoggingServiceTest to address flakiness by improving synchronization mechanisms for gRPC stream interactions.
• Synchronization Logic Update: Switched from relying on future completion to an explicit CountDownLatch for validating stream closures in testMultipleClientsSuccessfullyProcessed and testServerCloseHangsUpClients.
• Client Operation Assurance: Implemented awaiting on client futures to ensure all client operations are sent and streams are properly completed before proceeding with test assertions or server shutdown.
• Test Simplification: Simplified the stream creation and error handling logic in testMultipleClientsFailingIsHandledGracefullyByServer by removing unnecessary Callable tasks and BlockingQueue usage.

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[github-actions]

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R: @jrmccluskey added as fallback since no labels match configuration

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[jrmccluskey]

LGTM