Function retain_representative_indices 

pub fn retain_representative_indices<P: TrxScalar>(
    trx: &TrxFile<P>,
    params: &DuplicateRemovalParams,
) -> Vec<usize>

Compute the set of streamline indices to retain after duplicate removal.

Returns a sorted Vec<usize> of indices that are kept according to params. The returned indices can be passed to subset_streamlines to produce the deduplicated file.