Create a U-Net from a given architecture.
encoder
number of classes
image size
blur is used to avoid checkerboard artifacts at each layer.
blur final is specific to the last layer.
self_attention determines if we use a self attention layer at the third block before the end.
If y_range is passed, the last activations go through a sigmoid rescaled to that range.
last cross
bottle
activation
initializer
normalization type
None