perf: use walrus and python lint

Author: LeeEirc

src/mcp/server/sse.py

@@ -84,8 +84,7 @@ async def _remove_stream_writer(self, session_id: UUID) -> None:
         Remove the SSE session with the given session ID.
         """
         logger.debug(f"Remove SSE session with ID: {session_id}")
-        writer = self._read_stream_writers.pop(session_id, None)
-        if writer:
+        if writer := self._read_stream_writers.pop(session_id, None):
             await writer.aclose()
             logger.debug(f"Closed SSE session with ID: {session_id}")
         else:
@@ -132,10 +131,12 @@ async def sse_writer():
                             ),
                         }
                     )
+
         background_task = BackgroundTask(self._remove_stream_writer, session_id)
         async with anyio.create_task_group() as tg:
             response = EventSourceResponse(
-                content=sse_stream_reader, data_sender_callable=sse_writer,
+                content=sse_stream_reader,
+                data_sender_callable=sse_writer,
                 background=background_task,
             )
             logger.debug("Starting SSE response task")