Merge pull request #988 from PowerGridModel/fix/re-add-internal-is-nan-util

PGM-IO internal import resolution: Re add isnan internal import for PGM-IO, step 1

Author: nitbharambe

src/_utils.py

@@ -0,0 +1,11 @@
+# SPDX-FileCopyrightText: Contributors to the Power Grid Model project <powergridmodel@lfenergy.org>
+#
+# SPDX-License-Identifier: MPL-2.0
+
+"""
+This file contains helper functions for library-internal use only.
+Disclaimer!
+We do not officially support this functionality and may remove features in this library at any given time!
+"""
+
+from power_grid_model._core.utils import is_nan  # pylint: disable=unused-import