Improve pd.NA support with inspect_polygon

[hoxbro]

I'm not the biggest fan of this solution...

Fixes part of the problem observed in #6308 (comment)

import geopandas as gpd
import holoviews as hv
import pandas as pd
import spatialpandas as spd
from holoviews.operation.datashader import datashade, inspect_polygons
from shapely.geometry import MultiPolygon, Polygon

hv.extension("bokeh")

square1 = Polygon([(0, 0), (0, 1), (1, 1), (1, 0)])
square2 = Polygon([(2, 0), (2, 1), (3, 1), (3, 0)])
gdf = gpd.GeoDataFrame({"geometry": [square1, square2], "name": [pd.NA, "B"]})
sdf = spd.GeoDataFrame(gdf)

polys = hv.Polygons(sdf)
shaded = datashade(polys)
hover = inspect_polygons(shaded).opts(fill_color="red", tools=["hover"])
(shaded * hover)

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.

Project coverage is 88.50%. Comparing base (90f56c8) to head (a17de53).

Files with missing lines	Patch %	Lines
holoviews/core/data/spatialpandas.py	66.66%	1 Missing ⚠️
holoviews/core/util.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6362      +/-   ##
==========================================
- Coverage   88.50%   88.50%   -0.01%     
==========================================
  Files         323      323              
  Lines       68359    68363       +4     
==========================================
+ Hits        60502    60504       +2     
- Misses       7857     7859       +2     

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