Simplify on-demand sandbox worker sample wait

Replace the manual sleep loop with a blocking wait so the sample keeps the process alive without suggesting worker polling behavior.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: YunchuWang

examples/on_demand_sandbox/remote_worker.py

@@ -1,7 +1,7 @@
 """Remote worker image entrypoint for the Durable Task Scheduler on-demand sandbox activities sample."""
 
 import os
-import time
+import threading
 
 from durabletask import task
 from durabletask.azuremanaged.preview.on_demand_sandbox import OnDemandSandboxWorker
@@ -24,7 +24,6 @@ def _remote_hello(ctx: task.ActivityContext, name: str) -> str:
     worker.start()
     print("Python on-demand sandbox remote worker is running. Press Ctrl+C to stop.")
     try:
-        while True:
-            time.sleep(3600)
+        threading.Event().wait()
     except KeyboardInterrupt:
         pass