Add unit tests for data_utils.py

[nikhiltelkar2005-glitch]

Related Issue / Discussion:

Fixes Issue #166

Changes:

• New file: tests/test_data_utils.py — adds parametrized pytest unit tests for data_utils.py

Further Details:

Summary:

The file WeatherRoutingTool/algorithms/data_utils.py contained 5 testable units
(get_closest, distance, time_diffs, get_speed_from_arrival_time, and GridMixin)
but had zero test coverage — no test file referenced it anywhere.

This PR adds a new test file tests/test_data_utils.py with:

• pytest.fixture definitions for reusable inputs (numpy arrays, route coordinates, datetime objects)
• Parametrized tests for get_closest covering 5 edge cases (exact match, midpoint, beyond max, below min)
• Parametrized tests for get_speed_from_arrival_time covering 3 cases using unittest.mock.patch to mock RouteParams.get_per_waypoint_coords

Before: No tests existed for data_utils.py.
After: 8 passing tests covering get_closest and get_speed_from_arrival_time.

Dependencies:

No new dependencies required. Tests use only existing packages:
pytest, numpy, astropy, unittest.mock (standard library).

PR Checklist:

In the context of this PR, I:

• 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