Use optimized HTML model consistently

[philippjfr]

So it turns out I hadn't actually used the optimized HTML model consistently throughout so this PR should provide further speedups but also potential to break things.

@MarcSkovMadsen would you mind trying this out again?

[philippjfr]

Cc: @dharhas and @timothydmorton any chance you could also give this a spin on the LSST dashboard?

[MarcSkovMadsen]

Hi @philippjfr

Tested with success in Chrome and Firefox on Windows on all pages of the awesome-panel.org code.

Awesome!

[codecov]

Codecov Report

Merging #888 into master will increase coverage by 15.38%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #888       +/-   ##
==========================================
+ Coverage   69.72%   85.1%   +15.38%     
==========================================
  Files         104     104               
  Lines       10588   10590        +2     
==========================================
+ Hits         7382    9013     +1631     
+ Misses       3206    1577     -1629

Impacted Files	Coverage Δ
panel/tests/pane/test_holoviews.py	99.46% <100%> (ø)	⬆️
panel/tests/pane/test_vega.py	97.36% <100%> (ø)	⬆️
panel/tests/pane/test_markup.py	100% <100%> (ø)	⬆️
panel/pane/markup.py	93.28% <100%> (+42.28%)	⬆️
panel/tests/test_interact.py	100% <100%> (ø)	⬆️
panel/tests/pane/test_plot.py	100% <100%> (ø)	⬆️
panel/tests/test_param.py	99.84% <100%> (ø)	⬆️
panel/pane/image.py	77.94% <100%> (+24.26%)	⬆️
panel/compiler.py	6.25% <0%> (+6.25%)	⬆️
panel/pane/holoviews.py	86.47% <0%> (+11.22%)	⬆️
... and 46 more

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