Save model in PyTorch format

[Martins6]

First, congratulations on this package! It is amazing, and I think is a true advance for flexibility compared to AutoGL.

One thing that I've noticed in both AutoGL and here is that there's no way to save the model parameters / weights. I've tried to pickle the model, and it works, but when I compare the accuracy of the saved model and the unsaved one, I've got a pretty difference in the accuracy and in all the results. It seems that the weight saving is messing up in some floats.

Ideally, I think the community would benefit from generating a pure PyTorch model from the BoxModel class, so that it can be saved without a problem.

Thanks!