Adds SPDX license headers to utils.py

Author: AndrewSazonov

src/easydiffraction/display/utils.py

@@ -1,3 +1,6 @@
+# SPDX-FileCopyrightText: 2021-2025 EasyDiffraction contributors <https://github.com/easyscience/diffraction>
+# SPDX-License-Identifier: BSD-3-Clause
+
 from __future__ import annotations
 
 from typing import ClassVar