Function matching_stats_cost 

pub fn matching_stats_cost(a: &[char], sam_b: &Sam) -> u64

Cost probe: run only the matching-statistics scan of a vs sam_b (the unavoidable per-pair floor — RO’s first block is an LCS, Θ(|a|)) and return a checksum so it isn’t optimized out. Measures the pure scan throughput separate from the RO recursion.