fix(setup.py): Fix license deprecation

[C0rn3j]

Fixes this:

/usr/lib/python3.14/site-packages/setuptools/dist.py:765: SetuptoolsDeprecationWarning: License classifiers are deprecated.
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Please consider removing the following classifiers in favor of a SPDX license expression:
License :: OSI Approved :: BSD License
See https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license for details.
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!!