Python: docs(typing): add return type and docstring to store_results in utils/chat.py (#12910)

## Summary
- Added explicit return type `-> ChatHistory` to `store_results`.
- Added detailed docstring explaining parameters, return type, and
behavior.

## Why
- Improves static analysis, IDE support, and code readability.
- Makes the function self-documenting for new contributors.

## Testing
- No changes to runtime behavior.
- Existing test suite passes locally.

### Motivation and Context

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### Description

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### Contribution Checklist

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- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

---------

Co-authored-by: Tao Chen <[email protected]>

python/semantic_kernel/utils/chat.py

@@ -8,8 +8,16 @@ if TYPE_CHECKING:
     from semantic_kernel.contents.chat_message_content import ChatMessageContent
 
 
-def store_results(chat_history: ChatHistory, results: list["ChatMessageContent"]):
-    """Stores specific results in the context and chat prompt."""
+def store_results(chat_history: ChatHistory, results: list["ChatMessageContent"]) -> ChatHistory:
+    """Stores specific results in the context and chat prompt.
+
+    Args:
+        chat_history(ChatHistory): The current chat history instance.
+        results(list["ChatMessageContent"]): Messages to be stored in the history.
+
+    Returns:
+        ChatHistory: Updated chat history containing the new messages.
+    """
     for message in results:
         chat_history.add_message(message=message)
     return chat_history