Implement Player value_throttled

[philippjfr]

Fixed #587

[codecov]

Codecov Report

Merging #3756 (e4f0d47) into master (4a9b4d0) will decrease coverage by 0.00%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master    #3756      +/-   ##
==========================================
- Coverage   84.21%   84.21%   -0.01%     
==========================================
  Files         213      213              
  Lines       30993    31009      +16     
==========================================
+ Hits        26102    26114      +12     
- Misses       4891     4895       +4     

Flag	Coverage Δ
ui-tests	34.00% <41.66%> (+<0.01%)	⬆️
unitexamples-tests	77.11% <83.33%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
panel/widgets/player.py	78.57% <82.60%> (-1.14%)	⬇️
panel/models/widgets.py	100.00% <100.00%> (ø)

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