Python packaging classifiers as an Enum.

trove-classifiers encompass all valid PyPI classifiers, which can be found at
https://pypi.org/classifiers/.

The exact set of classifiers that is supported is pulled from
[trove-classifiers](https://pypi.org/project/trove-classifiers/) which is the
canonical source of PyPI's classifiers.

Trove classifiers were first defined in
[PEP-301](https://peps.python.org/pep-0301/#distutils-trove-classification)
and are metadata tags that can be added to python package distributions.