fix: aclose all async generators to fix OTel tracing context

See https://github.com/google/adk-python/issues/1670#issuecomment-3115891100

PiperOrigin-RevId: 794659547

contributing/samples/telemetry/main.py

@@ -46,13 +46,19 @@ async def main():
         role='user', parts=[types.Part.from_text(text=new_message)]
     )
     print('** User says:', content.model_dump(exclude_none=True))
-    async for event in runner.run_async(
+    # TODO - migrate try...finally to contextlib.aclosing after Python 3.9 is
+    # no longer supported.
+    agen = runner.run_async(
         user_id=user_id_1,
         session_id=session.id,
         new_message=content,
-    ):
-      if event.content.parts and event.content.parts[0].text:
-        print(f'** {event.author}: {event.content.parts[0].text}')
+    )
+    try:
+      async for event in agen:
+        if event.content.parts and event.content.parts[0].text:
+          print(f'** {event.author}: {event.content.parts[0].text}')
+    finally:
+      await agen.aclose()
 
   async def run_prompt_bytes(session: Session, new_message: str):
     content = types.Content(
@@ -64,14 +70,20 @@ async def main():
         ],
     )
     print('** User says:', content.model_dump(exclude_none=True))
-    async for event in runner.run_async(
+    # TODO - migrate try...finally to contextlib.aclosing after Python 3.9 is
+    # no longer supported.
+    agen = runner.run_async(
         user_id=user_id_1,
         session_id=session.id,
         new_message=content,
         run_config=RunConfig(save_input_blobs_as_artifacts=True),
-    ):
-      if event.content.parts and event.content.parts[0].text:
-        print(f'** {event.author}: {event.content.parts[0].text}')
+    )
+    try:
+      async for event in agen:
+        if event.content.parts and event.content.parts[0].text:
+          print(f'** {event.author}: {event.content.parts[0].text}')
+    finally:
+      await agen.aclose()
 
   start_time = time.time()
   print('Start time:', start_time)