[BREAKING] Python: Refactor workflow events to unified discriminated union pattern (#3690)

* Refactor events

* Merge main

* Fixes

* Cleanup

* Update samples and tests

* Remove unused imports

* PR feedback

* Merge main. Add properties for events to help typing

* Formatting

* Cleanup

* use builtins.type to avoid shadowing by WorkflowEvent.type attribute

* Final improvements

python/samples/getting_started/workflows/state-management/workflow_kwargs.py

@@ -2,9 +2,9 @@
 
 import asyncio
 import json
-from typing import Annotated, Any
+from typing import Annotated, Any, cast
 
-from agent_framework import ChatMessage, WorkflowOutputEvent, tool
+from agent_framework import ChatMessage, tool
 from agent_framework.openai import OpenAIChatClient
 from agent_framework.orchestrations import SequentialBuilder
 from pydantic import Field
@@ -27,7 +27,9 @@ Prerequisites:
 
 
 # Define tools that accept custom context via **kwargs
-# NOTE: approval_mode="never_require" is for sample brevity. Use "always_require" in production; see samples/getting_started/tools/function_tool_with_approval.py and samples/getting_started/tools/function_tool_with_approval_and_threads.py.
+# NOTE: approval_mode="never_require" is for sample brevity. Use "always_require" in production;
+# see samples/getting_started/tools/function_tool_with_approval.py
+# and samples/getting_started/tools/function_tool_with_approval_and_threads.py.
 @tool(approval_mode="never_require")
 def get_user_data(
     query: Annotated[str, Field(description="What user data to retrieve")],
@@ -118,8 +120,8 @@ async def main() -> None:
         additional_function_arguments={"custom_data": custom_data, "user_token": user_token},
         stream=True,
     ):
-        if isinstance(event, WorkflowOutputEvent):
-            output_data = event.data
+        if event.type == "output":
+            output_data = cast(list[ChatMessage], event.data)
             if isinstance(output_data, list):
                 for item in output_data:
                     if isinstance(item, ChatMessage) and item.text: