tests: await pending coroutine handlers

Receiver runner removal only guarantees coroutine handlers were scheduled on the handler loop. Wait for those invocations to complete before asserting the final call count.

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

Author: cartertinney

tests/unit/iothub/aio/test_async_handler_manager.py

@@ -463,6 +463,7 @@ async def test_handler_resolve_pending_items_before_handler_removal(
         handler,
         handler_checker,
         inbox,
+        async_poll_until,
     ):
         # Intercept inbox operations so the runner can be paused with work remaining
         original_get = inbox.get
@@ -519,6 +520,12 @@ def tracked_put(item):
         # Handler removal completes after the runner processes all pending items
         await asyncio.wait_for(removal_future, timeout=5)
 
+        # Coroutine handlers may still be completing on the handler loop
+        await async_poll_until(
+            lambda: handler_checker.handler_call_count >= 100,
+            timeout=BATCH_COMPLETION_TIMEOUT,
+        )
+
         # Despite removal, handler has been called for everything that was in the inbox at the
         # time of the removal
         assert handler_checker.handler_call_count == 100