Use isinstance in Python event examples

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: stephentoub

python/copilot/session.py

@@ -1128,11 +1128,10 @@ async def send_and_wait(
             Exception: If the session has been disconnected or the connection fails.
 
         Example:
-            >>> from typing import cast
             >>> from copilot.generated.session_events import AssistantMessageData
             >>> response = await session.send_and_wait("What is 2+2?")
-            >>> if response:
-            ...     print(cast(AssistantMessageData, response.data).content)
+            >>> if response and isinstance(response.data, AssistantMessageData):
+            ...     print(response.data.content)
         """
         idle_event = asyncio.Event()
         error_event: Exception | None = None
@@ -1178,13 +1177,12 @@ def on(self, handler: Callable[[SessionEvent], None]) -> Callable[[], None]:
             A function that, when called, unsubscribes the handler.
 
         Example:
-            >>> from typing import cast
             >>> from copilot.generated.session_events import AssistantMessageData, SessionErrorData
             >>> def handle_event(event):
-            ...     if event.type.value == "assistant.message":
-            ...         print(f"Assistant: {cast(AssistantMessageData, event.data).content}")
-            ...     elif event.type.value == "session.error":
-            ...         print(f"Error: {cast(SessionErrorData, event.data).message}")
+            ...     if isinstance(event.data, AssistantMessageData):
+            ...         print(f"Assistant: {event.data.content}")
+            ...     elif isinstance(event.data, SessionErrorData):
+            ...         print(f"Error: {event.data.message}")
             >>> unsubscribe = session.on(handle_event)
             >>> # Later, to stop receiving events:
             >>> unsubscribe()
@@ -1805,12 +1803,11 @@ async def get_messages(self) -> list[SessionEvent]:
             Exception: If the session has been disconnected or the connection fails.
 
         Example:
-            >>> from typing import cast
             >>> from copilot.generated.session_events import AssistantMessageData
             >>> events = await session.get_messages()
             >>> for event in events:
-            ...     if event.type.value == "assistant.message":
-            ...         print(f"Assistant: {cast(AssistantMessageData, event.data).content}")
+            ...     if isinstance(event.data, AssistantMessageData):
+            ...         print(f"Assistant: {event.data.content}")
         """
         response = await self._client.request("session.getMessages", {"sessionId": self.session_id})
         # Convert dict events to SessionEvent objects