Add .NET 8 support

[martincostello]

• Add support for .NET 8.
• Bump version to 6.6.0.

Resolves #2792 Resolves #2791 Resolves #2771 Resolves #2794

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 86.08%. Comparing base (4d5625f) to head (c29aeef).

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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2799      +/-   ##
==========================================
- Coverage   92.42%   86.08%   -6.35%     
==========================================
  Files          94       73      -21     
  Lines        3183     2795     -388     
  Branches      556      449     -107     
==========================================
- Hits         2942     2406     -536     
- Misses        241      389     +148     

Flag	Coverage Δ
Linux	86.08% <100.00%> (-6.35%)	:arrow_down:
Windows	86.08% <100.00%> (-6.35%)	:arrow_down:
macOS	86.08% <100.00%> (-6.35%)	:arrow_down:

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