Replace np.NaN with np.nan

[Hoxbro]

Numpy 2.0 support: https://numpy.org/devdocs/numpy_2_0_migration_guide.html

[codecov-commenter]

Codecov Report

Merging #5938 (10b07b1) into main (53f816e) will decrease coverage by 0.59%.
The diff coverage is 68.42%.

@@            Coverage Diff             @@
##             main    #5938      +/-   ##
==========================================
- Coverage   88.58%   87.99%   -0.59%     
==========================================
  Files         313      313              
  Lines       65100    65096       -4     
==========================================
- Hits        57668    57283     -385     
- Misses       7432     7813     +381     

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Files	Coverage Δ
holoviews/core/data/__init__.py	86.53% <100.00%> (ø)
holoviews/core/data/multipath.py	86.32% <100.00%> (ø)
holoviews/core/data/pandas.py	94.11% <100.00%> (ø)
holoviews/core/data/spatialpandas.py	87.46% <100.00%> (ø)
holoviews/core/data/xarray.py	89.63% <100.00%> (ø)
holoviews/element/graphs.py	85.43% <100.00%> (ø)
holoviews/element/stats.py	84.33% <100.00%> (ø)
holoviews/plotting/bokeh/util.py	67.03% <100.00%> (ø)
holoviews/plotting/mpl/plot.py	60.74% <100.00%> (ø)
holoviews/tests/core/data/test_multiinterface.py	99.41% <100.00%> (ø)
... and 31 more

... and 16 files with indirect coverage changes

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