[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/semantic-kernel-migration/orchestrations/handoff.py

@@ -8,12 +8,9 @@ from typing import cast
 
 from agent_framework import (
     ChatMessage,
-    HandoffBuilder,
-    HandoffUserInputRequest,
-    RequestInfoEvent,
     WorkflowEvent,
-    WorkflowOutputEvent,
 )
+from agent_framework.orchestrations import HandoffBuilder, HandoffUserInputRequest
 from agent_framework.azure import AzureOpenAIChatClient
 from azure.identity import AzureCliCredential
 from semantic_kernel.agents import Agent, ChatCompletionAgent, HandoffOrchestration, OrchestrationHandoffs
@@ -214,17 +211,17 @@ async def _drain_events(stream: AsyncIterable[WorkflowEvent]) -> list[WorkflowEv
     return [event async for event in stream]
 
 
-def _collect_handoff_requests(events: list[WorkflowEvent]) -> list[RequestInfoEvent]:
-    requests: list[RequestInfoEvent] = []
+def _collect_handoff_requests(events: list[WorkflowEvent]) -> list[WorkflowEvent]:
+    requests: list[WorkflowEvent] = []
     for event in events:
-        if isinstance(event, RequestInfoEvent) and isinstance(event.data, HandoffUserInputRequest):
+        if event.type == "request_info" and isinstance(event.data, HandoffUserInputRequest):
             requests.append(event)
     return requests
 
 
 def _extract_final_conversation(events: list[WorkflowEvent]) -> list[ChatMessage]:
     for event in events:
-        if isinstance(event, WorkflowOutputEvent):
+        if event.type == "output":
             data = cast(list[ChatMessage], event.data)
             return data
     return []