Struphy with cupy

[max-models]

Notes:

This MR is still pointing towards 318, but it will be merged into devel once finished (which will be after 318 has already been merged).

To run on my PC, I still need to do:

export ARRAY_BACKEND=cupy
export CUDA_PATH=/usr/local/cuda
export PATH=$CUDA_PATH/bin:$PATH

I am then running the Vlasov standard parameters

struphy params Vlasov
python params_Vlasov.py

To do

• Fix the need for setting CUDA path
• We have many cases of from numpy import xyz, this makes sense in pyccelized kernels since we will not be allowed to use cupy there. But in my current testing, but otherwise not.
• When calling a pyccelized kernel while using cupy, we can convert the arrays to numpy arrays, they should also be converted back to cupy arrays afterwards.

[max-models]

Moved to #93