fix `namespace_packages` deprecation warning
tomwer_venv_silx_2 payno@linpayno:~/Documents/dev/tomography/tomwer$ python setup.py bdist_wheel sdist
/home/payno/.local/share/virtualenvs/tomwer_venv_silx_2/lib/python3.11/site-packages/setuptools/config/setupcfg.py:293: _DeprecatedConfig: Deprecated config in `setup.cfg`
!!
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The namespace_packages parameter is deprecated, consider using implicit namespaces instead (PEP 420).
See https://setuptools.pypa.io/en/latest/userguide/declarative_config.html for details.
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