Dispatch CancelActivityNexusTask to worker via Nexus control queue

[rkannan82]

What changed?

This PR implements the dispatch logic for CancelActivityNexusTask. When the task is processed, it sends a CancelActivitiesRequest to the worker's Nexus control queue using the existing DispatchNexusTask RPC.
Changes
Task executor: transfer_queue_active_task_executor.go
processCancelActivityNexus: Main handler for the task
getWorkerControlQueueName: Looks up the worker's control queue from the worker registry via DescribeWorker API
dispatchActivityCancelToWorker: Builds task tokens and dispatches via DispatchNexusTask
Checks EnableActivityCancellationNexusTask dynamic config before processing
Returns NotFound error (triggering retry) if worker not found in registry
Control queue naming: Uses workerControlQueuePrefix (/temporal-sys/worker-commands) + worker_grouping_key from worker heartbeat
Batching: Single Nexus operation contains all activity task tokens for a worker

Why?

To support activity cancellation without activity heartbeat.

Overall flow:

• [https://github.com/Store worker_instance_key for an activity in mutable state #9231] Store worker instance key in ActivityInfo as part of RecordActivityTaskStarted call.
• [Add new transfer task type for cancelling activities using Nexus #9232] When user cancels a workflow, create 1 or more transfer tasks. Group all activities belonging to a worker into a transfer task (for efficiency).
• [This PR] Lookup the Nexus task queue for each worker, and send a Nexus operation for each transfer task.
• [SDK] Worker will receive this cancel task and cancel the running activities.

How did you test it?

• built
• run locally and tested manually
• covered by existing tests
• added new unit test(s)
• added new functional test(s)

Potential risks

Any change is risky. Identify all risks you are aware of. If none, remove this section.