Function global_node_connectivity 

pub fn global_node_connectivity(graph: &Graph) -> NodeConnectivityResult

Compute global node connectivity: minimum s-t node connectivity over all pairs.

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