Function build_tof_rt_grid_full 

pub fn build_tof_rt_grid_full(
    rt_frames: &RtFrames,
    window_group: Option<u32>,
) -> TofRtGrid

Build a dense TOF×RT grid (full matrix, summed over all scans).

• rows = rt_frames.scale.num_bins() (TOF bins)
• cols = rt_frames.frames.len() (RT frames)
• data[row * cols + col] = sum intensity in that (bin, frame) over all scans.