Switch MetricsSourceGenerator to IIncrementalGenerator

[Copilot]

Changed

• Migrated MetricsSourceGenerator from ISourceGenerator to IIncrementalGenerator to follow current Roslyn best practices and eliminate analyzer warnings RS1035 and RS1042
• Replaced ISyntaxReceiver pattern with incremental pipeline using CreateSyntaxProvider for syntax filtering and RegisterSourceOutput for code generation
• Changed diagnostic reporting to use SourceProductionContext instead of GeneratorExecutionContext

Removed

• Removed MetricsSyntaxReceiver.cs - filtering logic now integrated directly into generator using static predicates
• Removed dotnet_diagnostic.RS1035.severity = none and dotnet_diagnostic.RS1042.severity = none suppressions from .globalconfig
• Removed static constructor with hardcoded Handlebars assembly path

Benefits: The incremental generator only re-runs on changed files rather than the entire compilation, improving build performance. The pipeline properly caches intermediate results and supports parallel execution.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Switch to using IIncrementalGenerator for MetricsSourceGenerator - as non-incremental source generators should not be used</issue_title>
<issue_description>Remember to remove the following lines from .globalconfig:

dotnet_diagnostic.RS1035.severity = none
dotnet_diagnostic.RS1042.severity = none
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes Switch to using IIncrementalGenerator for MetricsSourceGenerator - as non-incremental source generators should not be used #371

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[github-actions]

NuGet packages for this PR, e.g. Cratis:
https://github.com/cratis/Fundamentals/packages/1655206?version=7.3.1-pr817.41d2739

[github-actions]

NuGet packages for this PR, e.g. Cratis:
https://github.com/cratis/Fundamentals/packages/1655206?version=7.3.1-pr817.41d2739

[github-actions]

NuGet packages for this PR, e.g. Cratis:
https://github.com/cratis/Fundamentals/packages/1655206?version=7.4.0-pr817.d5c64dd