Enhance affine transformation

[konstntokas]

• In xcube_resampling.reproject_dataset, the dataset is now clipped when the target
  grid-mapping covers less than 80% of the source grid-mapping, improving performance
  for reprojected cutouts.
• In xcube_resampling.affine_transform_dataset, resampling is now performed per
  spatial slice, ensuring that interpolation is applied only along the spatial axes
  and no longer across non-spatial dimensions (e.g., time).
• When prevent_nan_propagation=True, computation is now fully lazy. Previously, the
  implementation checked for NaN values in the source array, which triggered loading
  of the entire dataset into memory.

Checklist:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/
• Changes documented in CHANGES.md
• CI checks pass
• Test coverage remains or increases (target 100%)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.95%. Comparing base (530995f) to head (e014b7e).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #33      +/-   ##
==========================================
+ Coverage   98.65%   98.95%   +0.30%     
==========================================
  Files          20       20              
  Lines        2005     2018      +13     
==========================================
+ Hits         1978     1997      +19     
+ Misses         27       21       -6     

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