[BACKPORT 25.10] Added isCompleted check in getNumSpotInterruptions

[munishchouhan]

This PR will backport #6805 to 25.10

Prevents the deadlock because:

• Spot interruption counts are only meaningful after task completion
• Returns null immediately for non-completed tasks
• Avoids calling describeJob() and triggering the batching mechanism
• Only queries AWS Batch API when the task is completed and we actually need the spot interruption count

[pditommaso]

What about the version in master ?

[munishchouhan]

What about the version in master ?

there is another pr for that
#6805

[thalassemia]

I want to add that this was throttling task submission rate to about 1 every few seconds using the Google Batch executor. Specifically, notifyTaskSubmit() --> getTraceRecord() --> getNumSpotInterruptions() --> describeTask() --> getTaskStatus() --> apply() would repeatedly fail with a NotFoundException because Batch had not finished creating the job. This triggerred the retry policy until the job came online or five attempts were made. Thanks for the quick fix!