fix: TypeExtensions.GetMetadataName handles null Namespace (#4866)

[thomhurst]

Summary

• Fix TypeExtensions.GetMetadataName producing "null.TypeName" when a type is in the root (global) namespace
• When Type.Namespace is null or empty, the method now returns just type.Name instead of $"{type.Namespace}.{type.Name}"

Closes #4866

Test plan

• Verified the project builds successfully with dotnet build TUnit.Analyzers/TUnit.Analyzers.csproj
• Confirm analyzer correctly resolves metadata names for types in the root namespace
• Confirm analyzer still correctly resolves metadata names for types in named namespaces

[claude]

Code Review

The fix correctly handles the null namespace case in TUnit.Analyzers. However, there is an identical copy of the GetMetadataName method in the source generator that has not been updated:

TUnit.Core.SourceGenerator/Extensions/TypeExtensions.cs still contains the unfixed version:

public static string GetMetadataName(this Type type)
{
    return $"{type.Namespace}.{type.Name}";  // still produces "null.TypeName" for root-namespace types
}

This means types in the global/root namespace will still produce malformed metadata names ("null.TypeName") when processed through the source generator code path. The same one-line fix should be applied there:

return string.IsNullOrEmpty(type.Namespace) ? type.Name : $"{type.Namespace}.{type.Name}";

Reference:

TUnit/TUnit.Core.SourceGenerator/Extensions/TypeExtensions.cs

Lines 9 to 12 in eb0c53e

	public static string GetMetadataName(this Type type)
	{
	return $"{type.Namespace}.{type.Name}";
	}