Remove deprecated np.product

[hoxbro]

Removes warning seen in numpy 1.25:

❯ python -Wdefault -c "import numpy as np; np.product([1])"
sys:1: DeprecationWarning: `product` is deprecated as of NumPy 1.25.0, and will be removed in NumPy 2.0. Please use `prod` instead.

Also fixes a small bug in show_versions()

[codecov-commenter]

Codecov Report

Merging #5787 (e7e5140) into main (8df58d3) will decrease coverage by 0.03%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##             main    #5787      +/-   ##
==========================================
- Coverage   88.14%   88.12%   -0.03%     
==========================================
  Files         307      307              
  Lines       62850    62850              
==========================================
- Hits        55401    55388      -13     
- Misses       7449     7462      +13     

Flag	Coverage Δ
ui-tests	?

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Impacted Files	Coverage Δ
holoviews/element/util.py	82.21% <0.00%> (ø)
holoviews/util/_versions.py	35.29% <0.00%> (ø)
holoviews/core/data/grid.py	86.27% <100.00%> (ø)
holoviews/core/data/image.py	74.10% <100.00%> (ø)
holoviews/core/data/xarray.py	88.86% <100.00%> (ø)
holoviews/core/util.py	85.97% <100.00%> (ø)
holoviews/element/raster.py	78.97% <100.00%> (ø)

... and 2 files with indirect coverage changes

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