ENH: Add ngff-zarr multi-resolution registration example

Add Example 23 demonstrating a workflow that combines ngff-zarr
multi-resolution image pyramids with ITKElastix registration:

- Convert ITK images to ngff-zarr Multiscales via to_multiscales
- Register at a coarse resolution (rigid + affine + bspline)
- Convert Elastix results to itk.CompositeTransform
- Apply the transform at full resolution in parallel using
  dask.array.map_blocks with itk.resample_image_filter

Uses itk_image_to_ngff_image and ngff_image_to_itk_image to bridge
between ITK and ngff-zarr data representations.

Author: thewtex