Allow multiple edges of different types between nodes

[this-is-sofia]

The output of the FCI algorithm is a MAG with at most one edge between two nodes. However, to properly test the algorithm, it is helpful to test the inducing_path_exists function on ADMGs with possibly two different edge types between two nodes, a directed edge representing a direct effect and a bidirected edge representing a hidden confounder. (In a MAG, there would just be a directed edge in this case.)

Therefore, we should think about whether to implement this option. For now, we exclude tests that would need such an option in order to return the desired results, for example:

    def test_is_path_inducing_multiple_edges(self):
        graph = GraphManager()
        node1 = graph.add_node("test1", [1, 2, 3])
        node2 = graph.add_node("test2", [1, 2, 3])
        node3 = graph.add_node("test3", [1, 2, 3])
        graph.add_bidirected_edge(node1, node2, {"test": "test"})
        graph.add_bidirected_edge(node2, node3, {"test": "test"})
        graph.add_directed_edge(node2, node3, {"test": "test"})
        path = [(node1, node2), (node2, node3)]
        self.assertTrue(graph._is_path_inducing(path, node1, node3))