[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/orchestrations/sequential_agents.py

@@ -3,7 +3,7 @@
 import asyncio
 from typing import cast
 
-from agent_framework import ChatMessage, WorkflowOutputEvent
+from agent_framework import ChatMessage
 from agent_framework.azure import AzureOpenAIChatClient
 from agent_framework.orchestrations import SequentialBuilder
 from azure.identity import AzureCliCredential
@@ -48,7 +48,7 @@ async def main() -> None:
     # 3) Run and collect outputs
     outputs: list[list[ChatMessage]] = []
     async for event in workflow.run("Write a tagline for a budget-friendly eBike.", stream=True):
-        if isinstance(event, WorkflowOutputEvent):
+        if event.type == "output":
             outputs.append(cast(list[ChatMessage], event.data))
 
     if outputs: