Function stitch_im_peaks_flat_unordered_impl 

pub fn stitch_im_peaks_flat_unordered_impl(
    flat: Vec<Arc<ImPeak1D>>,
    params: &StitchParams,
) -> Vec<ImPeak1D>

Core stitching logic on ImPeak1D in TOF space.

• Buckets by (normed window_group, scan_bin, tof_bucket)
• Runs an in-bucket fold using compatible_fast + merge_into
• Then a single consolidation pass across bucket boundaries