Function compare_overhead 

pub fn compare_overhead(
    primitive: &ReductionOverhead,
    composite: &ReductionOverhead,
) -> ComparisonStatus

Compare two overheads across all common fields.

Returns Dominated if composite ≤ primitive on all common fields. Returns NotDominated if composite is worse on any common field. Returns Unknown if any common field’s expressions cannot be normalized into a comparable polynomial form or contain negative coefficients.