Function stacked_histogram_dense 

pub fn stacked_histogram_dense(
    t: &[i64],
    x: &[i64],
    y: &[i64],
    p: &[i64],
    grid: &[i64],
    delta_t_us: i64,
    nbins: usize,
    count_cutoff: u32,
    row_map: &[i64],
    col_map: &[i64],
    out_h: usize,
    out_w: usize,
) -> Array4<u8>

Build the dense stacked-histogram for one batch of windows.

All event arrays (t, x, y, p) cover the batch and are sorted by t (non-decreasing). grid holds the window END timestamps for this batch. row_map (length full H) and col_map (length full W) map a source row/column to its downsampled output index, or -1 if that row/column is dropped by the gather.

Returns an array of shape (n_windows, 2 * nbins, out_h, out_w) of u8.