stdlib: Add many missing dunder overrides (#7231)

stdlib/shelve.pyi

@@ -20,6 +20,7 @@ class Shelf(MutableMapping[str, _VT]):
     def __getitem__(self, key: str) -> _VT: ...
     def __setitem__(self, key: str, value: _VT) -> None: ...
     def __delitem__(self, key: str) -> None: ...
+    def __contains__(self, key: str) -> bool: ...  # type: ignore[override]
     def __enter__(self: Self) -> Self: ...
     def __exit__(
         self, type: type[BaseException] | None, value: BaseException | None, traceback: TracebackType | None