fix: TypeExtensions.GetMetadataName produces 'null.TypeName' for root namespace types

[thomhurst]

Description

File: TUnit.Analyzers/Extensions/TypeExtensions.cs (Line 11)

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

For root namespace types, type.Namespace is null, resulting in "null.TypeName".

Suggested Fix

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