Resolve "Visualize PG"

Closes #27 (closed)

b_asic/signal_flow_graph.py

@@ -627,7 +627,10 @@ class SFG(AbstractOperation):
             for port in ports:
                 for signal in port.signals:
                     pg.edge(port.operation.graph_id + '.' + str(port.index), signal.destination.operation.graph_id)
+                    pg.node(signal.destination.operation.graph_id, shape = 'square')
                 pg.edge(port.operation.graph_id, port.operation.graph_id + '.' + str(port.index))
+                pg.node(port.operation.graph_id, shape = 'square')
+
         pg.view()  
 
     def print_precedence_graph(self) -> None: