improve hint typing

Graph/graph/graph_1.py

@@ -27,11 +27,11 @@ class Node:
 
     _id = itertools.count(0)
 
-    def __init__(self):
+    def __init__(self) -> None:
         self.id: int = next(self._id)
         self.neighbors: Set['Node'] = set()
 
-    def __hash__(self):
+    def __hash__(self) -> int:
         # to be usable in set an object must be hashable
         # so we need to implement __hash__
         # which must returm an int uniq per object