Patch HoloViews client comm to ensure server comm is initialized

[philippjfr]

HoloViews has it's own code to initialize Jupyter comms here: https://github.com/holoviz/holoviews/blob/main/holoviews/plotting/renderer.py#L408

Sadly this means that the recent changes in #6229 to have the client Comm be responsible to initialize the server comm does not work for HoloViews. For now we therefore have to manually patch the client comm created by HoloViews with the required on_open callback. I will separately open a PR in HoloViews to add the on_open handler properly.

[philippjfr]

Here's the PR adding the on_open handler in HoloViews: holoviz/holoviews#6076

[codecov]

Codecov Report

Attention: 13 lines in your changes are missing coverage. Please review.

Comparison is base (3a3b1be) 84.17% compared to head (d523d7c) 22.29%.
Report is 4 commits behind head on main.

Files	Patch %	Lines
panel/io/notebook.py	23.52%	13 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #6234       +/-   ##
===========================================
- Coverage   84.17%   22.29%   -61.88%     
===========================================
  Files         301      301               
  Lines       45099    45118       +19     
===========================================
- Hits        37963    10061    -27902     
- Misses       7136    35057    +27921     

Flag	Coverage Δ
ui-tests	?
unitexamples-tests	22.29% <23.52%> (-49.56%)	⬇️

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