Add GPU detection within attacks

[suhacker1]

Is your feature request related to a problem? Please describe.
This should be integrated into all of the attacks. Users will no longer be required to explicitly state how many GPUs they are using. However, they should have the ability to do so. This should output something like:

GPU Available: True; GPU Used: False

This is motivated by the fact that the tests only work on a CPU due to GitHub Actions, so all tests must explicitly define that they are not using a GPU.

Describe the solution you'd like.
Explicit statements take priority over automated detection. This should turn off all GPU-specific behavior, especially .cuda methods.

Describe alternatives you've considered.
We could have separate tests on a GPU with a different CI. Self-hosted runners are not an option. We are open to alternatives.

Detail any additional context.
If you include a test for GPU behavior, it must be ignored by GitHub Actions somehow.

Potentially interesting links:

1. How PyTorch Lightning became the first ML framework to run continuous integration on TPUs
   
2. Effective testing for machine learning systems