Scallop with GPU doesn't work

[ldtho]

Hi @Liby99 ,
Thank you for the great work. I've had a really close look at your examples of how to train a scallop together with a Pytorch model.
However the whole model is on CPU, when I tried to run scallop on GPU it didn't work, and back-propagation has errors at backward() function (model is on GPU but scallop output is on CPU).
Would be great if you could provide guidance or a sample code.
Regards