Extracted tests and updated Pytorch version

[thomasahle]

This follows #7 in which we discussed updating the code to use PyTorch's complex tensors.

The pull request also extracts all tests into a tests/ directory, so it's easy to run unit tests. All 12 of which pass.

Other than there there are no changes, except auto formatting which my tools unfortunately don't allow me not to use.

[albertfgu]

Thanks for making such a comprehensive refactor!

I have a few questions about some of the changes

• Are the CUDA kernels no longer used? E.g. why are diag_mult_cuda/setup.py and hadamard_cuda/setup.py deleted?
• Is the code inside the scratch/ folder moved to tests, or deleted? I would prefer preserving the original code since it's clearly labeled as not part of the critical codepath but helps remind us of the progress that went into this project

It would have been ideal if the formatter changes were done in an independent commit to the actual changes, but I understand it's probably hard to factor that out so don't worry about it.