Update libcachesim/trace_reader.py

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: haochengxia

libcachesim/trace_reader.py

@@ -276,7 +276,7 @@ def go_back_one_req(self) -> None:
     def set_read_pos(self, pos: float) -> None:
         self._reader.set_read_pos(pos)
 
-    def get_working_set_size(self) -> Tuple[int, int]:
+    def get_working_set_size(self) -> tuple[int, int]:
         return cal_working_set_size(self._reader)
 
     def __iter__(self) -> Iterator[Request]: