replace setup.py with pyproject.toml

[shamilbi]

python -m pip install mintotp
...
Building wheels for collected packages: mintotp
  DEPRECATION: Building 'mintotp' using the legacy setup.py bdist_wheel mechanism, which will be removed in a future version.
    pip 25.3 will enforce this behaviour change.
    A possible replacement is to use the standardized build interface by setting the `--use-pep517` option, (possibly combined with `--no-build-isolation`),
    or adding a `pyproject.toml` file to the source tree of 'mintotp'.
    Discussion can be found at https://github.com/pypa/pip/issues/6334