non-isotropic patch size

[xiuliren]

it seems that the network only works while the patch size is all the same in XYZ.
When the patch size is 16x256x256, I got the following errors:

 File "/mnt/home/jwu/code/neutorch/neutorch/model/IsoRSUNet.py", line 187, in forward
    x = down_conv(x)
  File "/mnt/home/jwu/anaconda3/envs/cf/lib/python3.10/site-packages/torch/nn/modules/module.py", line 1194, in _call_impl
    return forward_call(*input, **kwargs)
  File "/mnt/home/jwu/anaconda3/envs/cf/lib/python3.10/site-packages/torch/nn/modules/container.py", line 204, in forward
    input = module(input)
  File "/mnt/home/jwu/anaconda3/envs/cf/lib/python3.10/site-packages/torch/nn/modules/module.py", line 1194, in _call_impl
    return forward_call(*input, **kwargs)
  File "/mnt/home/jwu/anaconda3/envs/cf/lib/python3.10/site-packages/torch/nn/modules/pooling.py", line 244, in forward
    return F.max_pool3d(input, self.kernel_size, self.stride,
  File "/mnt/home/jwu/anaconda3/envs/cf/lib/python3.10/site-packages/torch/_jit_internal.py", line 485, in fn
    return if_false(*args, **kwargs)
  File "/mnt/home/jwu/anaconda3/envs/cf/lib/python3.10/site-packages/torch/nn/functional.py", line 868, in _max_pool3d
    return torch.max_pool3d(input, kernel_size, stride, padding, dilation, ceil_mode)
RuntimeError: Given input size: (256x1x16x16). Calculated output size: (256x0x8x8). Output size is too small