Python: [Breaking] Remove WorkflowCompletedEvent, introduce workflow output and migrate to ctx.yield_output() + a huge refactoring (#845)

* Introduce input and output types for executor and workflow

* WorkflowOutputContext handles two types

* Remove can_handle_types from Executor

* Update validation

* Move workflow executor

* Move workflow executor

* Fix issues in WorkflowExecutor

* refactor executor

* update execute signature to create workflow context within Executor

* fix simple sub workflow test; fix validation

* fix output types in WorkflowExecutor

* fix issue in Executor handling of SubWorkflowRequestInfo

* update tests to use proper workflow output

* update orchestration patterns to use output

* Update sample -- not finished

* Update python/packages/main/tests/workflow/test_workflow_states.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Update python/packages/main/tests/workflow/test_concurrent.py

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* address comments

* WorkflowOutputContext --> WorkflowContext

* remove WorkflowCompletedEvent

* update samples

* Update doc string for important classes; update WorkflowExecutor to support concurrent execution

* use Never instead of None for default type

* Update usage of WorkflowContext[None to WorkflowContext[Never

* address comments

* remove filter for None

* address comments, minor fixes

* quality of life improvement on interceptor types

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

python/packages/main/tests/workflow/test_sequential.py

@@ -15,8 +15,10 @@ from agent_framework import (
     Role,
     SequentialBuilder,
     TextContent,
-    WorkflowCompletedEvent,
     WorkflowContext,
+    WorkflowOutputEvent,
+    WorkflowRunState,
+    WorkflowStatusEvent,
     handler,
 )
 
@@ -66,15 +68,20 @@ async def test_sequential_agents_append_to_context() -> None:
 
     wf = SequentialBuilder().participants([a1, a2]).build()
 
-    completed: WorkflowCompletedEvent | None = None
+    completed = False
+    output: list[ChatMessage] | None = None
     async for ev in wf.run_stream("hello sequential"):
-        if isinstance(ev, WorkflowCompletedEvent):
-            completed = ev
+        if isinstance(ev, WorkflowStatusEvent) and ev.state == WorkflowRunState.IDLE:
+            completed = True
+        elif isinstance(ev, WorkflowOutputEvent):
+            output = ev.data  # type: ignore[assignment]
+        if completed and output is not None:
             break
 
-    assert completed is not None
-    assert isinstance(completed.data, list)
-    msgs: list[ChatMessage] = completed.data  # type: ignore[assignment]
+    assert completed
+    assert output is not None
+    assert isinstance(output, list)
+    msgs: list[ChatMessage] = output
     assert len(msgs) == 3
     assert msgs[0].role == Role.USER and "hello sequential" in msgs[0].text
     assert msgs[1].role == Role.ASSISTANT and (msgs[1].author_name == "A1" or True)
@@ -89,14 +96,19 @@ async def test_sequential_with_custom_executor_summary() -> None:
 
     wf = SequentialBuilder().participants([a1, summarizer]).build()
 
-    completed: WorkflowCompletedEvent | None = None
+    completed = False
+    output: list[ChatMessage] | None = None
     async for ev in wf.run_stream("topic X"):
-        if isinstance(ev, WorkflowCompletedEvent):
-            completed = ev
+        if isinstance(ev, WorkflowStatusEvent) and ev.state == WorkflowRunState.IDLE:
+            completed = True
+        elif isinstance(ev, WorkflowOutputEvent):
+            output = ev.data  # type: ignore[assignment]
+        if completed and output is not None:
             break
 
-    assert completed is not None
-    msgs: list[ChatMessage] = completed.data  # type: ignore[assignment]
+    assert completed
+    assert output is not None
+    msgs: list[ChatMessage] = output
     # Expect: [user, A1 reply, summary]
     assert len(msgs) == 3
     assert msgs[0].role == Role.USER