Fix integer truncation in temperature.fuentes by forcing float dtype …

[Chirag3841]

• [ x] Closes Integer/float bug in pvlib.temperature.fuentes #2608
• [ x] I am familiar with the contributing guidelines
• [x ] I attest that all AI-generated material has been vetted for accuracy and is in compliance with the pvlib license
• [x ] Tests added
• Updates entries in docs/sphinx/source/reference for API changes.
• Adds description and name entries in the appropriate "what's new" file in docs/sphinx/source/whatsnew for all changes. Includes link to the GitHub Issue with :issue:`num` or this Pull Request with :pull:`num`. Includes contributor name and/or GitHub username (link with :ghuser:`user`).
• New code is fully documented. Includes numpydoc compliant docstrings, examples, and comments where necessary.
• [x ] Pull request is nearly complete and ready for detailed review.
• Maintainer: Appropriate GitHub Labels (including remote-data) and Milestone are assigned to the Pull Request and linked Issue.

Summary

Fix integer truncation in pvlib.temperature.fuentes.

The function created the internal array using np.zeros_like(poa_global),
which inherits the dtype of the input. When integer inputs were provided,
intermediate floating-point temperatures were truncated when written into
the array.

This patch forces the internal array to use a floating-point dtype:
tmod_array = np.zeros_like(poa_global, dtype=float)

Updated expected values in test_fuentes_timezone to reflect the corrected
behavior and added a regression test test_fuentes_int_vs_float to ensure
integer and float inputs produce identical results.