first successful tests of cupy JIT; waiting for !393 to continue

src/pystencils/backend/exceptions.py

src/pystencils/backend/jit/__init__.py

src/pystencils/backend/jit/gpu_cupy.py

src/pystencils/backend/kernelcreation/cpu_optimization.py

src/pystencils/backend/kernelfunction.py

src/pystencils/backend/platforms/cuda.py

src/pystencils/config.py

tests/nbackend/kernelcreation/test_domain_kernels.py