test(langgraph): use monotonic clock in flaky streaming test (#7477)

Switches test_sync_streaming_with_functional_api to time.monotonic() for
both emitted task timestamps and observed arrival times so the assertion
is based on a monotonic clock instead of wall time. This makes the
streaming timing check less flaky on systems where time.time() can jump
or lack sufficient precision.

Created with [Deep Agents
CLI](https://docs.langchain.com/oss/python/deepagents/cli/overview)
using gpt-5.4 (provider: openai).

libs/langgraph/tests/test_pregel.py

@@ -6271,7 +6271,7 @@ def test_sync_streaming_with_functional_api() -> None:
     @task()
     def slow() -> dict:
         time.sleep(time_delay)  # Simulate a delay of 10 ms
-        return {"tic": time.time()}
+        return {"tic": time.monotonic()}
 
     @entrypoint()
     def graph(inputs: dict) -> list:
@@ -6284,7 +6284,7 @@ def test_sync_streaming_with_functional_api() -> None:
     for chunk in graph.stream({}):
         if "slow" not in chunk:  # We'll just look at the updates from `slow`
             continue
-        arrival_times.append(time.time())
+        arrival_times.append(time.monotonic())
 
     assert len(arrival_times) == 2
     delta = arrival_times[1] - arrival_times[0]