Log rejection of polls from recently-shutdown workers (#9811)

## What
Add an Info-level log when a poll is rejected because the worker is in
the shutdown cache. Follows up on #9545.

## Why
The shutdown-worker cache returns `errNoTasks` silently, making cache
rejections indistinguishable from normal empty polls. This log helps
operators debug cases where a worker's polls aren't getting tasks
post-shutdown.

## How did you test it?
Built.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: rkannan82

service/matching/matching_engine.go

@@ -2859,6 +2859,12 @@ func (e *matchingEngineImpl) pollTask(
 	// returned to the handler before a context timeout error is generated.
 	workerInstanceKey := pollMetadata.workerInstanceKey
 	if workerInstanceKey != "" && e.shutdownWorkers.Get(workerInstanceKey) != nil {
+		e.logger.Info("Rejecting poll from recently-shutdown worker",
+			tag.WorkflowNamespaceID(partition.NamespaceId()),
+			tag.WorkflowTaskQueueName(partition.TaskQueue().Name()),
+			tag.WorkflowTaskQueueType(partition.TaskType()),
+			tag.NewStringTag("worker-instance-key", workerInstanceKey),
+		)
 		return nil, false, errNoTasks
 	}