remove old connections in substitute node reuse

src/kyupy/circuit.py

@@ -370,6 +370,8 @@ class Circuit:
         if designated_cell is not None:
             node.kind = designated_cell.kind
             node_map[designated_cell] = node
+            node.ins = GrowingList()
+            node.outs = GrowingList()
         else:
             node.remove()
         ios = set(impl.io_nodes)