chore: add GUT test framework

addons/gut/test/resources/awaiting_post_run_script.gd

@@ -0,0 +1,15 @@
+extends 'res://addons/gut/hook_script.gd'
+
+var awaited = false
+
+func run():
+	print('!! --- post-run script awaiting --- !!')
+	
+	var awaiter = GutUtils.Awaiter.new()
+	gut.add_child(awaiter)
+	awaiter.wait_seconds(1)
+	await awaiter.timeout
+	awaited = true
+	awaiter.queue_free()
+	
+	print('!! --- post-run script has successfully awaited --- !!')