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/update/GdUnitPatch.gd

@@ -0,0 +1,20 @@
+class_name GdUnitPatch
+extends RefCounted
+
+const PATCH_VERSION = "patch_version"
+
+var _version :GdUnit4Version
+
+
+func _init(version_ :GdUnit4Version) -> void:
+	_version = version_
+
+
+func version() -> GdUnit4Version:
+	return _version
+
+
+# this function needs to be implement
+func execute() -> bool:
+	push_error("The function 'execute()' is not implemented at %s" % self)
+	return false