Fix num_strides in uresnet_lonely (and other models potentially)

[Temigo]

We agreed that num_strides should describe the number of downsampling operations (i.e. number of strides). This is not currently the case, at least not in uresnet_lonely: for example a spatial size of 768 leads to 6 feature maps of size [768, 384, 192, 96, 48, 24], which according to the above should be described at num_strides: 5 (currently resulting from num_strides: 6). We should update the implementation to match the description above.