✅ Roslyn: Get file scoped namespace

using System;

namespace TestNamespaceSpace;

public class TestClass 
{

}

var root = syntaxTree.GetRoot();
var controllerClasses = root.DescendantNodes().OfType<ClassDeclarationSyntax>()
                            .Where(IsControllerClass);

var @namespace = root.DescendantNodesAndSelf().OfType<NamespaceDeclarationSyntax>().FirstOrDefault();