Update sizing of Panel models dynamically

[philippjfr]

Fixes #5971

[codecov]

Codecov Report

Attention: 16 lines in your changes are missing coverage. Please review.

Comparison is base (a9a5067) 83.11% compared to head (a031789) 72.64%.

Files	Patch %	Lines
panel/tests/ui/pane/test_markup.py	0.00%	16 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #6054       +/-   ##
===========================================
- Coverage   83.11%   72.64%   -10.48%     
===========================================
  Files         295      295               
  Lines       43960    43976       +16     
===========================================
- Hits        36539    31948     -4591     
- Misses       7421    12028     +4607     

Flag	Coverage Δ
ui-tests	?
unitexamples-tests	72.64% <0.00%> (-0.13%)	⬇️

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