CuPy-specific implementation of `random`

Currently Cubed's implementation of `random` just uses NumPy (since random number generation is not part of the Array API) and converts to the backend array type (e.g. CuPy). It would be better to use something like `cupy.random.Generator` and `cupy.random.Philox4x3210` as a special case when the backend is CuPy.