iteration_slice with step-size for GPU-kernels

Step-size of iteration_slice is ignored for GPU-kernels.

import pystencils as ps

dh = ps.create_data_handling(domain_size=(5, 5), periodicity=True, default_target="gpu")

iteration_slice = ps.make_slice[1:-1:2, 1:-1:2]
config = ps.CreateKernelConfig(target=dh.default_target, iteration_slice=iteration_slice)

field = dh.add_array("a")

assign = ps.Assignment(field.center, 1.0)
kernel = ps.create_kernel(assign, config=config).compile()

dh.fill(field.name, 0, ghost_layers=True)

if config.target == ps.enums.Target.GPU:
  dh.to_gpu(field.name)

dh.run_kernel(kernel)

if config.target == ps.enums.Target.GPU:
  dh.to_cpu(field.name)

print(dh.gather_array(field.name, ghost_layers=True))

results in

[[0. 0. 0. 0. 0. 0. 0.]
 [0. 1. 1. 1. 1. 1. 0.]
 [0. 1. 1. 1. 1. 1. 0.]
 [0. 1. 1. 1. 1. 1. 0.]
 [0. 1. 1. 1. 1. 1. 0.]
 [0. 1. 1. 1. 1. 1. 0.]
 [0. 0. 0. 0. 0. 0. 0.]]