Function slbw_cross_sections_for_range 

pub fn slbw_cross_sections_for_range(
    range: &ResonanceRange,
    energy_ev: f64,
    awr: f64,
    target_spin: f64,
) -> (f64, f64, f64, f64)

Compute SLBW cross-sections for a single resolved resonance range.

This is the per-range workhorse called by both slbw_cross_sections (which iterates over all ranges) and the unified dispatcher in reich_moore::cross_sections_for_range.

Returns (total, elastic, capture, fission) in barns.