Fix numpy array syntax in scaling.py and update tests

[r0hansaxena]

• Closes scaling.py Numpy function arg bug #2614
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• Tests added
• Updates entries in docs/sphinx/source/reference for API changes.
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Description

This PR addresses Issue #2614, where latlon_to_xy in pvlib/scaling.py was incorrectly handling discrete scaling factors due to a numpy syntax error. Instead of passing a list to np.array(), the code passed separate arguments, leading to incorrect coordinate scaling.

Proposed Changes

1. Fixed pvlib/scaling.py: Corrected the np.array call to properly scale latitude and longitude by their respective factors.
2. Updated tests/test_scaling.py: Recalculated and updated the expected values in the positions(), expect_cs_smooth(), and expect_vr() fixtures. The previous expectations were based on the buggy code's output.
3. Whatsnew entry: Added a summary of the fix to the v0.15.1.rst changelog.

Verification Results

All tests in tests/test_scaling.py now pass locally with the corrected calculations.