[Bug]: rustworkx fails to handle non-contiguous node numbering

[thierry-martinez]

The following code raises KeyError in rxgraphviews.get_node_index when use_rustworkx is True:

    @pytest.mark.parametrize("use_rustworkx", [False, True])
    def test_pauli_non_contiguous(self, use_rustworkx) -> None:
        pattern = Pattern(input_nodes=[0])
        pattern.extend([
            N(node=2, state=PlanarState(plane=Plane.XY, angle=0.0)),
            E(nodes=(0, 2)),
            M(node=0, plane=Plane.XY, angle=0.0, s_domain=set(), t_domain=set())
        ])
        pattern.perform_pauli_measurements(use_rustworkx=use_rustworkx)

The bug seems to be between RXGraphState.neighbors, RXGraphState.subgraphs and RXGraphState.local_complement: the indexes returned by neighbors are in the rustworkx numbering, whereas local_complement calls subgraphs on these nodes, which expects them to be in the graphix numbering.

A fix could be to add a idx_to_num mapping in rxgraphviews and convert neighbors in the graphix numbering.

Related issues: #206 (problem with rxgraphviews).