chore(client): add gdUnit4 test framework addon

Vendor gdUnit4 for Godot 4 client testing (D-030).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/addons/gdUnit4/src/network/GdUnitTask.gd

@@ -0,0 +1,25 @@
+class_name GdUnitTask
+extends RefCounted
+
+const TASK_NAME = "task_name"
+const TASK_ARGS = "task_args"
+
+var _task_name :String
+var _fref :Callable
+
+
+func _init(task_name :String,instance :Object,func_name :String) -> void:
+	_task_name = task_name
+	if not instance.has_method(func_name):
+		push_error("Can't create GdUnitTask, Invalid func name '%s' for instance '%s'" % [instance, func_name])
+	_fref = Callable(instance, func_name)
+
+
+func name() -> String:
+	return _task_name
+
+
+func execute(args :Array) -> GdUnitResult:
+	if args.is_empty():
+		return _fref.call()
+	return _fref.callv(args)