fn next_candidate<G0, G1>(
st: &mut (Vf2State<'_, G0>, Vf2State<'_, G1>),
) -> Option<(G0::NodeId, G1::NodeId, OpenList)>where
G0: GetAdjacencyMatrix + GraphProp + NodeCompactIndexable + IntoNeighborsDirected,
G1: GetAdjacencyMatrix + GraphProp + NodeCompactIndexable + IntoNeighborsDirected,