Function build_rt_marginal 

pub fn build_rt_marginal(
    frames: &[FrameBinView],
    rt_lo: usize,
    rt_hi: usize,
    bin_lo: usize,
    bin_hi: usize,
    im_lo: usize,
    im_hi: usize,
) -> Vec<f32>

Build RT marginal (len = frames in [rt_lo..rt_hi]), using (bin,scan) window