Improve startup, error handling and shutdown of Jupyter kernels

[philippjfr]

No description provided.

[codecov]

Codecov Report

Merging #4364 (468979b) into main (95c244b) will decrease coverage by 0.96%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #4364      +/-   ##
==========================================
- Coverage   82.79%   81.84%   -0.96%     
==========================================
  Files         240      240              
  Lines       34637    34650      +13     
==========================================
- Hits        28677    28358     -319     
- Misses       5960     6292     +332     

Flag	Coverage Δ
ui-tests	38.28% <0.00%> (-0.05%)	⬇️
unitexamples-tests	72.70% <0.00%> (-1.05%)	⬇️

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Impacted Files	Coverage Δ
panel/io/jupyter_executor.py	0.00% <0.00%> (ø)
panel/io/jupyter_server_extension.py	0.00% <0.00%> (ø)
panel/__main__.py	0.00% <0.00%> (-100.00%)	⬇️
panel/tests/command/test_serve.py	23.80% <0.00%> (-64.77%)	⬇️
panel/command/__init__.py	14.60% <0.00%> (-53.94%)	⬇️
panel/tests/widgets/test_terminal.py	36.44% <0.00%> (-22.43%)	⬇️
panel/widgets/terminal.py	50.47% <0.00%> (-20.48%)	⬇️
panel/io/__init__.py	75.00% <0.00%> (-20.00%)	⬇️
panel/command/serve.py	16.59% <0.00%> (-19.09%)	⬇️
panel/io/document.py	49.69% <0.00%> (-6.75%)	⬇️
... and 11 more

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