Do not use static options for default quantizer constructors.

[JimBobSquarePants]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
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• I have provided test coverage for my change (where applicable)

Description

While investigating #1583 I realized that the static default options in all the quantizer instances could be overwritten which we should not allow.

I've also ensured we throw a better exception should someone use the default current struct instances to dither.

[codecov]

Codecov Report

Merging #1721 (3e56885) into master (c084b5f) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1721   +/-   ##
=======================================
  Coverage   84.40%   84.41%           
=======================================
  Files         822      822           
  Lines       36056    36063    +7     
  Branches     4203     4207    +4     
=======================================
+ Hits        30434    30443    +9     
  Misses       4802     4802           
+ Partials      820      818    -2     

Flag	Coverage Δ
unittests	84.41% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...arp/Processing/Processors/Dithering/ErrorDither.cs	100.00% <100.00%> (+1.96%)	⬆️
...p/Processing/Processors/Dithering/OrderedDither.cs	100.00% <100.00%> (+2.00%)	⬆️
...cessing/Processors/Quantization/OctreeQuantizer.cs	100.00% <100.00%> (ø)
...essing/Processors/Quantization/PaletteQuantizer.cs	100.00% <100.00%> (ø)
...Processors/Quantization/WebSafePaletteQuantizer.cs	100.00% <100.00%> (ø)
.../Processors/Quantization/WernerPaletteQuantizer.cs	100.00% <100.00%> (ø)
.../Processing/Processors/Quantization/WuQuantizer.cs	100.00% <100.00%> (ø)

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[antonfirsov]

LGTM, thanks!

[antonfirsov]

Wait ... should we do the same checks in ApplyPaletteDither ?

[JimBobSquarePants]

Wait ... should we do the same checks in ApplyPaletteDither ?

Yuuuuuuuup. Missed that, good catch! Done.