Report Activity result when the Activity leaves the interrupt flag set

[samarth70]

What was changed

ActivityWorker now clears the thread's interrupt flag around the call that reports an Activity result, and restores it afterwards.

Why

An Activity can return with the interrupt flag raised, either because it caught an InterruptedException, restored the flag and carried on, or because it never noticed the flag at all. gRPC's blocking stubs abort when Thread.interrupted() is set (io.grpc.stub.ClientCalls#blockingUnaryCall), which the SDK already notes in MultiThreadedPoller.PollTask. So the RespondActivityTaskCompleted call issued immediately after the Activity returns fails, and the result is never reported. The Activity then times out and the Workflow observes a failure even though the Activity completed successfully.

Reproduced on main (v1.38.0) with an Activity that raises the flag and returns "done":

WARN  i.t.internal.worker.ActivityWorker - Failure during reporting of activity result
	at io.temporal.internal.worker.ActivityWorker$TaskHandlerImpl.sendReply(ActivityWorker.java:406)
	at io.temporal.internal.worker.ActivityWorker$TaskHandlerImpl.handleActivity(ActivityWorker.java:357)
...
io.temporal.failure.ActivityFailure: Activity with activityType='Execute' failed: 'Activity task timed out'

This is the general case of the problem fixed for one specific caller in #722; that PR removed an interrupt the SDK itself was raising, while this makes the reporting path resilient to a flag raised by user code.

The flag is restored in a finally once reporting is done, so it still reaches the thread pool and continues to work for shutdown, per the approach suggested in the issue.

Checklist

1. Closes Activities that return with interrupted flag should be successfully reported as Completed #731

2. How was this tested:

Added io.temporal.activity.ActivityInterruptedFlagTest with two cases matching the two scenarios described in the issue: an Activity that never noticed the flag, and one that caught an InterruptedException, restored the flag and returned a result. Both assert the Workflow receives the Activity's return value.

Both fail on unmodified main (the Workflow fails with Activity task timed out as above) and pass with this change. ./gradlew :temporal-sdk:test --tests "io.temporal.activity.ActivityInterruptedFlagTest" reports tests="2" failures="0" errors="0", and :temporal-sdk:spotlessCheck passes.

3. Any docs updates needed?

No.