Improve Code Quality

[iamcarbon]

• Make RgbPaletteEntry a readonly struct
• Makes UafVersion a readonly struct
• Makes AuthenticationDevicePublicKeyOutputs immutable
• Makes PublicKeyCredentialDescriptor immutable
• Fixes a misspelled class name

[iamcarbon]

@abergs @aseigler Ready for feedback / review.

[codecov-commenter]

Codecov Report

Merging #405 (d22e731) into master (53caf81) will increase coverage by 0.26%.
The diff coverage is 60.00%.

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@@            Coverage Diff             @@
##           master     #405      +/-   ##
==========================================
+ Coverage   74.61%   74.88%   +0.26%     
==========================================
  Files          92       92              
  Lines        2714     2731      +17     
  Branches      453      456       +3     
==========================================
+ Hits         2025     2045      +20     
+ Misses        575      573       -2     
+ Partials      114      113       -1     

Impacted Files	Coverage Δ
Src/Fido2/AuthenticatorAssertionResponse.cs	43.04% <ø> (ø)
...ido2/Objects/DevicePublicKeyAuthenticatorOutput.cs	41.37% <ø> (ø)
Src/Fido2.Models/Metadata/UafVersion.cs	45.45% <45.45%> (-54.55%)	⬇️
Src/Fido2.Models/Metadata/RgbPaletteEntry.cs	50.00% <50.00%> (-50.00%)	⬇️
...desiredMetadataStatusFido2VerificationException.cs	60.00% <50.00%> (ø)
Src/Fido2/AuthenticatorAttestationResponse.cs	76.00% <50.00%> (ø)
...o2.Models/Objects/PublicKeyCredentialDescriptor.cs	80.00% <77.77%> (+17.50%)	⬆️
.../AuthenticationExtensionsDevicePublicKeyOutputs.cs	83.33% <83.33%> (-16.67%)	⬇️
Src/Fido2/Objects/AttestedCredentialData.cs	85.10% <100.00%> (+2.96%)	⬆️

... and 1 file with indirect coverage changes

[iamcarbon]

@abergs Ping. Let me know if you have any feedback.

[abergs]

@iamcarbon Will merge #379 before this one.