stdlib: add __slots__ (#14611)

stdlib/socket.pyi

@@ -1300,6 +1300,7 @@ class _SendableFile(Protocol):
     # def fileno(self) -> int: ...
 
 class socket(_socket.socket):
+    __slots__ = ["__weakref__", "_io_refs", "_closed"]
     def __init__(
         self, family: AddressFamily | int = -1, type: SocketKind | int = -1, proto: int = -1, fileno: int | None = None
     ) -> None: ...