Function global_minimum_node_cut 

pub fn global_minimum_node_cut(graph: &Graph) -> MinimumNodeCutResult

Compute global minimum node cut: the smallest set of nodes whose removal disconnects the graph.

Algorithm 11 from Esfahanian: pick min-degree node v, start with cut = neighbors(v), check non-neighbors of v, then non-adjacent pairs of neighbors of v. Matches networkx.algorithms.connectivity.minimum_node_cut(G).