`gt:gpu` slowdown on `gtpy` v1 due to change in allocation

[FlorianDeconinck]

gt4py v1 removes the Storage class and allow any __array_interface__ describing object to be bound. Unfortunately, the default cupy allocation used in our model has a bad stride (should have unit stride) leading to performance decrease in the backend.

Potential solution:

• use gt4py provided allocator (and optimized for the backend)
• make sure striding in our GPU allocation is unit