Shift-E on point elements doesn't retain annotations (i.e. additional DataFrame columns)

Thanks for this awesome package!

I just wanted to quickly leave the following report here:

After viewing a points element in napari and saving it back to the SpatialData object using "Shift-E", annotations are not retained.

Reproducer:

from spatialdata import SpatialData
from spatialdata.models import PointsModel
import pandas as pd

sdata = SpatialData()

sdata['points'] = PointsModel.parse(
        pd.DataFrame({
            'x': [1, 2],
            'y': [3, 4],
            'category': ['A', 'B'],
        }),
    )

sdata['points'].columns # Index(['x', 'y', 'category'], dtype='object')

from napari_spatialdata import Interactive

interactive = Interactive(sdata)
interactive.add_element("points", "global")

# press Shift-E

sdata['points'].columns # sdata['points'].columns # no longer contains column 'category' (no longer contains column 'category')

Versions used:

napari_spatialdata.__version__: 0.5.4.post0
spatialdata.__version__: 0.4.0

Start with the Interactive(sdata) setup and its add_element("points", "global") entry point, then trace what Shift-E invokes when saving the points element. Run the provided pandas and PointsModel reproducer, and verify that the category column remains in sdata['points'].columns after the save.