Function random_3sat 

pub fn random_3sat(vars: usize, num_clauses: usize, seed: u64) -> DimacsCnf

A random 3-SAT instance: num_clauses clauses of three distinct variables with random signs, over vars variables, from a seeded SplitMix64 stream (reproducible — no wall-clock). Near the clause/variable ratio 4.26 these are the canonical hard, non-symmetric benchmarks — the general-instance control where raw CDCL quality (not symmetry breaking) decides the race.