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/test/mocker/resources/ClassWithVariables.gd

@@ -0,0 +1,40 @@
+@tool
+class_name ClassWithVariables
+extends Node
+
+enum{
+	A,
+	B,
+	C
+}
+
+enum ETYPE 	{
+	EA,
+	EB
+	}
+
+# Declare member variables here. Examples:
+var a := 2
+var b := "text"
+
+# Declare some const variables
+const T1 = 1
+
+const T2 = 2
+
+signal source_changed( text:String )
+
+@onready var name_label := load("res://addons/gdUnit4/test/mocker/resources/ClassWithNameA.gd")
+
+@export var path: NodePath = ".."
+
+class ClassA:
+	var x := 1
+	# some comment
+	func foo()->String:
+		return ""
+
+
+func foo(_value :int = T1) -> void:
+	var _c := str(a) + b
+	pass