add (overwrite with) mypy stubs, if available

stdlib/3/functools.pyi

@@ -0,0 +1,12 @@
+# Stubs for functools
+
+# NOTE: These are incomplete!
+
+from typing import Callable, Any, Optional
+
+# TODO implement as class; more precise typing
+# TODO cache_info and __wrapped__ attributes
+def lru_cache(maxsize: Optional[int] = 100) -> Callable[[Any], Any]: ...
+
+# TODO more precise typing?
+def wraps(func: Any) -> Any: ...