Function certify_linear_rigidity 

pub fn certify_linear_rigidity(
    num_vars: usize,
    clauses: &[Vec<Lit>],
) -> Option<LinearRigidityCert>

Certify the linear (GF(2)) rigidity of F under the standard budget — None on any refusal (no parity structure, or over budget). See certify_linear_rigidity_within for the documented refusal.