Function best_ms1_for_each_ms2_any 

pub fn best_ms1_for_each_ms2_any(
    ms1: &[ClusterResult1D],
    ms2: &[ClusterResult1D],
    pairs: &[(usize, usize)],
    mode: AssignmentMode<'_>,
) -> Vec<Option<usize>>

Switch between geometric and XIC assignment.