Function compute_instability 

pub fn compute_instability<N, E>(
    graph: &Graph<N, E>,
) -> Vec<NamespaceInstability>
where
    N: ClassNode,
    E: EdgeKind,

Compute Ca / Ce / I for every namespace in graph.

Only inter-namespace edges count toward Ca/Ce — intra-namespace edges (a class depending on a sibling in the same package) do not contribute to package-level coupling. Output is sorted by namespace name for determinism.