Function certify_pigeonhole_unsat 

pub fn certify_pigeonhole_unsat(
    pigeons: u128,
    holes: u128,
) -> Option<CountingCert>

Certify PHP(pigeons → holes) UNSAT by pure counting, in O(1). Some iff pigeons > holes (Hall violated by the full pigeon set); None otherwise (feasible — a perfect matching can exist).