Python: Fixed middleware and multimodal input samples (#4022)

* Fix streaming branch in weather override middleware sample

The streaming branch of weather_override_middleware only prefixed the
original weather data via a transform hook instead of replacing the
content with the 'perfect weather' override like the non-streaming
branch does. Replace with a new ResponseStream that yields the override
content as ChatResponseUpdate chunks.

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

* Fixed exception handling middleware sample

* Fixed runtime context delegation middleware example

* Fixed multimodal input examples

* Small update

---------

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

python/samples/02-agents/multimodal_input/azure_chat_multimodal.py

@@ -9,7 +9,7 @@ from azure.identity import AzureCliCredential
 
 def create_sample_image() -> str:
     """Create a simple 1x1 pixel PNG image for testing."""
-    # This is a tiny red pixel in PNG format
+    # This is a tiny yellow pixel in PNG format
     png_data = "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8/5+hHgAHggJ/PchI7wAAAABJRU5ErkJggg=="
     return f"data:image/png;base64,{png_data}"
 
@@ -32,7 +32,7 @@ async def test_image() -> None:
         ],
     )
 
-    response = await client.get_response(message)
+    response = await client.get_response([message])
     print(f"Image Response: {response}")