[python] Fix output type when exporting PointCloudDataFrame to SpatialData points

[jp-dark]

The previous implementation of to_spatial_data_points was exporting data to a pandas DataFrame, but SpatialData expected a dask DataFrame. This type error was not caught in the tests using spatialdata.models.PointsModel.validate. This fixes the tests to check the type along with additional validataion by using spatialdata.models.get_model instead of the validate methods, and updates the exporter to return the correct type.

[johnkerl]

🚢

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 85.89%. Comparing base (c4fe227) to head (37d4702).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3408      +/-   ##
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+ Coverage   85.83%   85.89%   +0.05%     
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  Files          55       55              
  Lines        6191     6195       +4     
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+ Hits         5314     5321       +7     
+ Misses        877      874       -3     

Flag	Coverage Δ
python	85.89% <50.00%> (+0.05%)	⬆️

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Components	Coverage Δ
python_api	85.89% <50.00%> (+0.05%)	⬆️
libtiledbsoma	∅ <ø> (∅)