chore: add GUT test framework

addons/gut/scratch/demo_cyclic_ref.gd

@@ -0,0 +1,19 @@
+extends SceneTree
+
+
+
+class CyclicRefClass:
+	var other_thing = null
+
+
+func _init() -> void:
+	var cyclic_ref_a = CyclicRefClass.new()
+	var cyclic_ref_b = CyclicRefClass.new()
+	cyclic_ref_a.other_thing = cyclic_ref_b
+	cyclic_ref_b.other_thing = cyclic_ref_a
+
+	# cyclic_ref_a.other_thing = null
+	# cyclic_ref_b.other_thing = null
+
+	await create_timer(.5).timeout
+	quit()