Function gamp_awgn 

fn gamp_awgn(
    dip: &mut DipoleOp,
    plan: &WaveletPlan,
    cfg: &GampCfg,
    st: &mut GampState,
    lambda: &mut f64,
    tau_w_1_in: f64,
    der_1st: &[Complex64],
    weight_vect: &[f64],
    y: &[Complex64],
    wave_mask: &[bool],
) -> f64

One GAMP call with single-Gaussian (AWGN) noise. Returns updated tau_w_1.