auto_sigma_prior needs to depend on magnification

Created by: cabouman

The current versions of auto_sigma_prior(), auto_sigma_x(), and auto_sigma_p() were directly ported from SVMBIR, so they do not depend on magnification. I think this means that the value of the estimated values of sigma_x and sigma_p will be wrong for large values of magnification. However, we will want to double check this first by running some examples.

We will probably need to replace line 183 with: typical_img_value = np.average(sino, weights=sino_indicator) / (num_det_channels * delta_pixel_detector/magnification)

Once this is tested, we will want to port these routines to SVMBIR since with the fan geometry SVMBIR also has magnification.