Allow 3D array processing and Cupy compatability

[PinkShnack]

I would like to have nrefocus capable of processing 3D array inputs and be compatible with Cupy, similar to qpretrieve.

• The qpretrieve issues are Move from 2D to 3D array operations: breaking changes qpretrieve#9 and Add Cupy FFTs as FFTFilter option qpretrieve#10.
• The PRs are Move from 2d to 3d array operations qpretrieve#12, Add Cupy as optional dep and as FFTFilter qpretrieve#16 and Draft: Make codebase ndarray backend agnostic qpretrieve#18.

I already have a working version over in https://github.com/PinkShnack/nrefocus/tree/feat/3d_gpu_array_processing that works nicely with qpretrieve and some cupy phase unwrapping that will be soon added as a repo to the RI-imaging Org.

Todo

• Allow 3D data input (i would limit to 2d and 3d single channel data)
• Add Cupy FFT as a refocus option, along with the organisation as an optional dependency.
• Make the codebase ndarray backend agnostic. (xp.array)