Add worker control task protos for activity cancellation

Add WorkerControlTasks, WorkerControlTask, and CancelActivityTask to worker/v1/message.proto
for pushing control messages to workers via Nexus control queue.

Author: rkannan82

temporal/api/worker/v1/message.proto

@@ -11,6 +11,7 @@ option csharp_namespace = "Temporalio.Api.Worker.V1";
 
 import "google/protobuf/duration.proto";
 import "google/protobuf/timestamp.proto";
+import "temporal/api/common/v1/message.proto";
 import "temporal/api/deployment/v1/message.proto";
 import "temporal/api/enums/v1/common.proto";
 
@@ -139,3 +140,29 @@ message PluginInfo {
     // The version of the plugin, may be empty.
     string version = 2;
 }
+
+// Container for batching multiple control tasks delivered to a worker in one Nexus operation.
+message WorkerControlTasks {
+    repeated WorkerControlTask tasks = 1;
+}
+
+// A single control task for a worker.
+message WorkerControlTask {
+    // Timestamp when this task was created.
+    google.protobuf.Timestamp create_time = 1;
+
+    oneof task {
+        CancelActivityTask cancel_activity = 2;
+    }
+}
+
+// Request to cancel running activities on this worker.
+message CancelActivityTask {
+    // The workflow execution that owns the activities.
+    temporal.api.common.v1.WorkflowExecution workflow_execution = 1;
+    // The scheduled event IDs of activities to cancel.
+    // If empty, cancel all activities for this workflow running on this worker.
+    repeated int64 scheduled_event_ids = 2;
+    // Human-readable reason for cancellation.
+    string reason = 3;
+}