Update _Timer.

Author: tkem

stubs/cachetools/cachetools/__init__.pyi

@@ -52,8 +52,11 @@ class RRCache(Cache[_KT, _VT]):
 class _TimedCache(Cache[_KT, _VT]):
     def __init__(self, maxsize: float, timer: Callable[..., _TT], getsizeof: Callable[[_VT], float] | None): ...
 
-    class _Timer(AbstractContextManager[_TT]):
+    class _Timer:
+        def __init__(self, timer: Callable[[], _TT]) -> None: ...
         def __call__(self) -> _TT: ...
+        def __enter__(self) -> _TT: ...
+        def __exit__(self, *exc: Unused) -> None: ...
         def __getattr__(self, name: str) -> Any: ...
 
     @property