Improve Code Quality

[iamcarbon]

A quick tidying utilizing .NET8.0 features.

• Use HashSizeInBytes
• Use .NET 8.0 throw helpers
• Use FrozenDictionary to improve lookups
• Use required properties
• Use throw helpers
• Improve nullability annotations

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 62.00000% with 19 lines in your changes are missing coverage. Please review.

Project coverage is 74.62%. Comparing base (9ad038b) to head (f742369).

Files	Patch %	Lines
...ls/Metadata/DisplayPNGCharacteristicsDescriptor.cs	0.00%	7 Missing ⚠️
Src/Fido2.Models/Metadata/EcdaaTrustAnchor.cs	0.00%	6 Missing ⚠️
Src/Fido2.Models/Metadata/BiometricStatusReport.cs	0.00%	2 Missing ⚠️
Src/Fido2.Models/AssertionOptions.cs	66.66%	1 Missing ⚠️
Src/Fido2.Models/Metadata/ExtensionDescriptor.cs	50.00%	1 Missing ⚠️
...Fido2.Models/Metadata/PatternAccuracyDescriptor.cs	0.00%	1 Missing ⚠️
...c/Fido2/Metadata/Fido2MetadataServiceRepository.cs	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #509      +/-   ##
==========================================
+ Coverage   74.49%   74.62%   +0.13%     
==========================================
  Files          98       98              
  Lines        2639     2633       -6     
  Branches      445      442       -3     
==========================================
- Hits         1966     1965       -1     
+ Misses        570      567       -3     
+ Partials      103      101       -2     

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[iamcarbon]

@aseigler @abergs Ready for review / feedback.

[abergs]

All good! Thanks @iamcarbon for nice contributions and sorry for the long wait to get this in.