Add REUSE compliance

Signed-off-by: Thijs Baaijen <[email protected]>

Author: Thijss

tests/unit/visualizer/test_parsers.py

@@ -1,3 +1,7 @@
+# SPDX-FileCopyrightText: Contributors to the Power Grid Model project <[email protected]>
+#
+# SPDX-License-Identifier: MPL-2.0
+
 from power_grid_model_ds._core.model.arrays import NodeArray, LineArray
 from power_grid_model_ds._core.visualizer.parsers import parse_node_array, parse_branch_array
 from tests.integration.visualizer_tests import CoordinatedNodeArray