Fix transform_to_data_extent converting labels to images

[aeisenbarth]

This PR ensures transform_to_data_extent preserves the data type of labels and does not convert them to images. Here, I chose the most minimal solution to pass the (missing) parameter return_regions_as_labels=True and override its default of False.

Meanwhile, @quentinblampey has already documented the parameter return_regions_as_labels in rasterize.

Closes #783

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.84%. Comparing base (6694c91) to head (014eb37).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #791   +/-   ##
=======================================
  Coverage   91.84%   91.84%           
=======================================
  Files          45       45           
  Lines        6893     6893           
=======================================
  Hits         6331     6331           
  Misses        562      562           

Files with missing lines	Coverage Δ
src/spatialdata/_core/operations/_utils.py	92.15% <ø> (ø)

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[aeisenbarth]

CI is failing, probably due to a mismatch of Zarr and AnnData versions ("cannot import name 'Array' from 'zarr.core'").