Better IDiagnosticWriter API

[erri120]

Requires #1082.

• makes IDiagnosticWriter a singleton
• requires StringBuilder to be passed as state

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 22.00000% with 39 lines in your changes are missing coverage. Please review.

Project coverage is 54.27%. Comparing base (a3c2f41) to head (138e259).
Report is 2 commits behind head on main.

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1085      +/-   ##
==========================================
+ Coverage   54.21%   54.27%   +0.06%     
==========================================
  Files         672      671       -1     
  Lines       22211    22200      -11     
  Branches     1713     1714       +1     
==========================================
+ Hits        12042    12050       +8     
+ Misses       9773     9759      -14     
+ Partials      396      391       -5     

Flag	Coverage Δ
Linux	53.59% <22.00%> (+0.06%)	⬆️
Windows	53.54% <22.00%> (+0.06%)	⬆️
clean_environment_tests	54.25% <22.00%> (+0.04%)	⬆️
macOS	53.05% <22.00%> (+0.06%)	⬆️

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

Files	Coverage Δ
...cs/DiagnosticTemplateIncrementalSourceGenerator.cs	84.71% <100.00%> (+0.09%)	⬆️
src/NexusMods.App.UI/Services.cs	98.77% <100.00%> (-0.01%)	⬇️
...bstractions.Games.Diagnostics/IDiagnosticWriter.cs	0.00% <0.00%> (ø)
...I/Controls/Diagnostics/DiagnosticEntryViewModel.cs	0.00% <0.00%> (ø)
...p.UI/DiagnosticSystem/LoadoutReferenceFormatter.cs	0.00% <0.00%> (ø)
...s.App.UI/DiagnosticSystem/ModReferenceFormatter.cs	0.00% <0.00%> (ø)
...Mods.App.UI/DiagnosticSystem/NamedLinkFormatter.cs	0.00% <0.00%> (ø)
.../Diagnostics/Details/DiagnosticDetailsViewModel.cs	0.00% <0.00%> (ø)
...rols/Diagnostics/DiagnosticEntryDesignViewModel.cs	0.00% <0.00%> (ø)
...sMods.Abstractions.Games.Diagnostics/Diagnostic.cs	26.92% <0.00%> (-4.90%)	⬇️
... and 1 more

... and 4 files with indirect coverage changes

[Sewer56]

Does exactly as says on the tin