Update to .NET 8

[joegoldman2]

Fixes #419.
Fixes #497.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (b597d18) 74.44% compared to head (4a34cc8) 74.45%.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #503   +/-   ##
=======================================
  Coverage   74.44%   74.45%           
=======================================
  Files          99       98    -1     
  Lines        2677     2666   -11     
  Branches      455      445   -10     
=======================================
- Hits         1993     1985    -8     
+ Misses        580      578    -2     
+ Partials      104      103    -1     

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[abergs]

This looks fair (just holding off merging for a bit)

[abergs]

@iamcarbon Since you've been prepping for .net 8, please feel free to do a review. If no comments I'll bring this.

Thanks for the contribution @joegoldman2

[iamcarbon]

Looks good here! Thanks @joegoldman2

This also enables us to use frozen collections, collection builders, init only members (that can remain serializable by System.Text.Json), required properties, and some other nice things from .NET 8.0.