[Bug]: Mark TestMetadataGenerator code with generated code attribute

[dosolkowski-work]

Description

The code generated by TUnit.Core.SourceGenerator.Generators.TestMetadataGenerator is not marked with the [GeneratedCode] attribute, which makes it harder to exclude from code coverage reports.

Expected Behavior

All code generated by source generators would be marked with [GeneratedCode]. If appropriate, it could also be marked with [ExcludeFromCodeCoverage] as well.

Actual Behavior

The code, which is generated in the TUnit.Generated namespace, is not marked with any attributes to signify it is auto-generated.

Steps to Reproduce

Use <EmitCompilerGeneratedFiles>true</EmitCompilerGeneratedFiles> in a project file to see the generated code and note it is not marked with attributes.

TUnit Version

1.13.0

.NET Version

.NET 10

Operating System

Windows

IDE / Test Runner

Other (please specify in additional context)

Error Output / Stack Trace

Additional Context

This happens during build, not during test execution, although the impact mostly affects code coverage reports.

IDE-Specific Issue?

• I've confirmed this issue occurs when running via dotnet test or dotnet run, not just in my IDE