De-parameterize the options Keywords objects

[philippjfr]

The Keywords object is used to store the allowable keywords for an options object. It was Parameterized but is such a simple object that there is really no need and since it is created very, very frequently this turned out to be a very, very expensive thing to create. In many situations the creation of these objects could account for anywhere between 10-30% of the time to display anything.

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 1 line in your changes missing coverage. Please review.

Project coverage is 88.51%. Comparing base (96317ad) to head (c5beb15).
Report is 1 commits behind head on main.

Files	Patch %	Lines
holoviews/core/options.py	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6314      +/-   ##
==========================================
- Coverage   88.51%   88.51%   -0.01%     
==========================================
  Files         323      323              
  Lines       68093    68093              
==========================================
- Hits        60272    60271       -1     
- Misses       7821     7822       +1     

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[philippjfr]

ffmpeg issue unrelated and fixed separately.