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/update/GdUnitUpdateTest.gd

@@ -0,0 +1,44 @@
+# GdUnit generated TestSuite
+class_name GdUnitUpdateTest
+extends GdUnitTestSuite
+
+# TestSuite generated from
+const GdUnitUpdate = preload('res://addons/gdUnit4/src/update/GdUnitUpdate.gd')
+
+# Store original content to restore after test execution
+const testResource := "res://addons/gdUnit4/test/update/resources/ExampleSceneWithUids.txt"
+var original_content: String
+
+func before() -> void:
+	var file := FileAccess.open(testResource, FileAccess.READ)
+	original_content = file.get_as_text()
+	file.close()
+
+
+func after() -> void:
+	var file := FileAccess.open(testResource, FileAccess.WRITE)
+	file.store_string(original_content)
+	file.close()
+
+func after_test() -> void:
+	clean_temp_dir()
+
+
+func test_remove_uids_from_file() -> void:
+	var update_tool: GdUnitUpdate = auto_free(GdUnitUpdate.new())
+
+	# start uid patching
+	update_tool.remove_uids_from_file(testResource)
+
+	# Verify
+	var patched_content := get_content(testResource)
+	var expected_content := get_content("res://addons/gdUnit4/test/update/resources/ExampleScenePached.txt")
+	assert_str(patched_content).is_equal(expected_content)
+
+
+func get_content(resource: String) -> String:
+	var file := FileAccess.open(resource, FileAccess.READ)
+	var content := file.get_as_text()
+	file.close()
+
+	return content