Add Xarray gpu support

[sandorkertesz]

Requires the develop branch of earthkit-utils.

This PR:

• added the array_backend option to to_xarray() and made the previously used array_module option deprecated
• made the array_backend option work in to_xarray() both for generating lazy loaded and in-memory Xarrays
• the current code internally is always using a "patched" array namespace from earthkit-utils. This should be revisited.
• improved the dtype option for to_xarray(). Now it accepts str for all backends and internally converts it into an array-api-compat dtype object.
• added the to_device() method to the earthkit Xarray accessor to move the array values to the specified device and array backend

New notebook: docs/examples/xarray_cupy.ipynb

[codecov-commenter]

Codecov Report

❌ Patch coverage is 56.86275% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.61%. Comparing base (6d58af7) to head (432805b).
⚠️ Report is 299 commits behind head on develop.

Files with missing lines	Patch %	Lines
tests/xr_engine/test_xr_torch.py	40.54%	22 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #745      +/-   ##
===========================================
- Coverage    90.76%   90.61%   -0.15%     
===========================================
  Files          171      172       +1     
  Lines        13050    13080      +30     
  Branches       625      625              
===========================================
+ Hits         11845    11853       +8     
- Misses        1015     1037      +22     
  Partials       190      190              

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