Update packaging license metadata

[saisharan0103]

Updates pyproject.toml for #3802 by replacing the deprecated PEP 621 license table form with the SPDX string form:

• Changed license = {text = "BSD-3-Clause"} to license = "BSD-3-Clause".
• Removed the redundant License :: OSI Approved :: BSD License Trove classifier.

This addresses newer setuptools warnings during sdist builds about deprecated license metadata. No source code behavior changes are included.

ruff check pyproject.toml reports no new findings on the changed files.
Ran pytest -x locally with no new failures.

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