Fix histogram operation on Ibis data

[maximlt]

While working on holoviz/hvplot#997 I realized that (perhaps unsurprisingly) some Ibis code paths were broken or not working as expected. I fixed some bugs related to API changes in ibis after version 5.0 and a bug in the histogram computation when density=True.

[codecov-commenter]

Codecov Report

Merging #5929 (ef407f4) into main (adbfe2c) will increase coverage by 0.03%.
The diff coverage is 90.38%.

@@            Coverage Diff             @@
##             main    #5929      +/-   ##
==========================================
+ Coverage   88.42%   88.45%   +0.03%     
==========================================
  Files         313      313              
  Lines       65160    65209      +49     
==========================================
+ Hits        57619    57683      +64     
+ Misses       7541     7526      -15     

Flag	Coverage Δ
ui-tests	23.27% <32.69%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
holoviews/core/data/ibis.py	82.01% <100.00%> (+4.85%)	⬆️
holoviews/operation/element.py	75.59% <75.00%> (+1.04%)	⬆️
holoviews/tests/conftest.py	86.66% <80.00%> (-3.34%)	⬇️
holoviews/tests/operation/test_operation.py	98.57% <93.75%> (-0.63%)	⬇️

... and 1 file with indirect coverage changes

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[maximlt]

When this eventually gets merged after review/changes, is it possible to get a quick dev release? I'd need one to merge holoviz/hvplot#997 (unless I pin ibis there).

[Hoxbro]

LGTM 👍