Improve many __(a)exit__ annotations (#9696)

stubs/cachetools/cachetools/__init__.pyi

@@ -1,4 +1,4 @@
-from _typeshed import IdentityFunction
+from _typeshed import IdentityFunction, Unused
 from collections.abc import Callable, Iterator, MutableMapping, Sequence
 from contextlib import AbstractContextManager
 from typing import Any, Generic, TypeVar, overload
@@ -66,7 +66,7 @@ class _TimedCache(Cache[_KT, _VT]):
         def __init__(self, timer: Callable[[], float]) -> None: ...
         def __call__(self) -> float: ...
         def __enter__(self) -> float: ...
-        def __exit__(self, *exc: object) -> None: ...
+        def __exit__(self, *exc: Unused) -> None: ...
 
     @property
     def timer(self) -> _Timer: ...