fix: ignore redundant interrupted exceptions

[toddbaert]

The awaitTermination on retryScheduler was added in #1734 as boilerplate when we removed some Thread.sleeps. The awaitTermination calls in the shutdown chain throw InterruptedException when the SDK's shutdown timeout fires and sets the interrupt flag. This is harmless but noisy.

This PR adds a ShutdownUtils.awaitTerminationQuietly() utility that catches InterruptedException and restores the interrupt flag. It's applied to all three awaitTermination sites in the shutdown chain. This is safe because nothing further up the call stack relies on InterruptedException from shutdown; the interrupt flag is preserved so any subsequent interruptible operations still behave. I added some basic tests for this util.

Also adds synchronized(this) to SyncStreamQueueSource.shutdown() to prevent grpcComponents from being swapped by reinitializeChannelComponents() mid-shutdown as Gemini pointed out, there's a possible race here.

I manually tested this with a very contrived test to confirm my understanding, but I don't think adding the test will add much value long term and it's weird to test for the absence of a line-of-code IMO.

[gemini-code-assist]

Code Review

This pull request modifies the shutdown method in SyncStreamQueueSource.java by removing the call to awaitTermination for the retryScheduler. The scheduler is now immediately followed by the gRPC channel connector shutdown after shutdownNow is invoked. I have no feedback to provide as there were no review comments to evaluate.

[toddbaert]

/gemini review.

[gemini-code-assist]

Code Review

This pull request removes the termination wait for the retry scheduler during the shutdown process of SyncStreamQueueSource. A review comment identifies a potential race condition between the shutdown and reinitialization methods, suggesting that the shutdown logic should be synchronized to prevent leaking gRPC channels.

[toddbaert]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a ShutdownUtils utility to standardize the handling of InterruptedException during component shutdown across the flagd provider. By utilizing awaitTerminationQuietly, the implementation now suppresses the exception while correctly restoring the thread's interrupt flag. As a result, the shutdown() method signatures in several classes and interfaces, such as FlagdProvider, ChannelConnector, and Storage, have been updated to remove the throws InterruptedException declaration. Additionally, synchronization was added to the shutdown logic in SyncStreamQueueSource to improve thread safety. I have no feedback to provide as the changes are consistent and follow best practices for handling thread interruptions.