[test] Add unit tests for algorithms/data_utils.py

[adity1raut]

Related Issue / Discussion:

• Fixes Issue [test] Add unit tests for WeatherRoutingTool/algorithms/data_utils.py #166

Changes:

• New tests/test_data_utils.py — unit test file for
  WeatherRoutingTool/algorithms/data_utils.py

Further Details:

Summary:

data_utils.py contains 5 testable units (get_closest, distance,
time_diffs, get_speed_from_arrival_time, and GridMixin) that had
zero test coverage before this PR.

This PR adds tests/test_data_utils.py with 44 unit tests organized
into pytest classes with shared fixtures and pytest.mark.parametrize.
Key assertions use analytically known WGS-84 geodesic values
(1° longitude on the equator ≈ 111 319.49 m) so tests are fully
self-contained and do not depend on external data files.

Class	Function(s) covered	Tests
TestGetClosest	get_closest()	7
TestDistance	distance()	7
TestTimeDiffs	time_diffs()	7
TestGetSpeedFromArrivalTime	get_speed_from_arrival_time()	9
TestGridMixin	index_to_coords, coords_to_index, get_shuffled_cost	10

Before: no tests for data_utils.py.
After: 44 passing unit tests with full coverage of all public functions.

Dependencies:

No new dependencies. All imports (numpy, pytest, xarray,
astropy) are already listed in requirements.test.txt.

PR Checklist:

In the context of this PR, I:

• have (already previously) filled the 52North Contributor License Agreement and received positive feedback on this matter
• have filled the 52North Contributor License Agreement and am waiting for feedback
• provide unit tests embedded in the WRT test framework (WeatherRoutingTool/tests) that allow the simple testing of the new/modified functionalities. All (previous and new) unit tests execute without new error messages.
• ensure that the code formatter runs without errors/warnings
• ensure that my changes follow the WRT's guidelines for contributing at the time of the contribution

[kdemmich]

Thank you for your PR. We appreciate the time and effort that was put into it. Please be aware that we require to follow 52 North's CLA guidelines for all PRs and, in particular, fill the 52°North Contributor License Agreement. As long as this has not been filled, I can not assign you to any issues or merge any PRs. Please don't hesitate to contact me in case of related questions.