Fix incorrect build-system requirements

[kurtmckee]

This change fixes incorrect build-system requirements and resolves deprecation warnings thrown in CI when building using the latest setuptools versions. [recent example]

/tmp/build-env-gfscc8yk/lib/python3.11/site-packages/setuptools/config/_apply_pyprojecttoml.py:82: SetuptoolsDeprecationWarning: `project.license` as a TOML table is deprecated
!!

        ********************************************************************************
        Please use a simple string containing a SPDX expression for `project.license`. You can also use `project.license-files`. (Both options available on setuptools>=77.0.0).

        By 2026-Feb-18, you need to update your project and remove deprecated calls
        or your builds will no longer be supported.

        See https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license for details.
        ********************************************************************************

!!
  corresp(dist, value, root_dir)
/tmp/build-env-gfscc8yk/lib/python3.11/site-packages/setuptools/config/_apply_pyprojecttoml.py:61: SetuptoolsDeprecationWarning: License classifiers are deprecated.
!!

        ********************************************************************************
        Please consider removing the following classifiers in favor of a SPDX license expression:

        License :: OSI Approved :: MIT License

        See https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license for details.
        ********************************************************************************

!!
  dist._finalize_license_expression()
/tmp/build-env-gfscc8yk/lib/python3.11/site-packages/setuptools/dist.py:759: SetuptoolsDeprecationWarning: License classifiers are deprecated.
!!

        ********************************************************************************
        Please consider removing the following classifiers in favor of a SPDX license expression:

        License :: OSI Approved :: MIT License

        See https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license for details.
        ********************************************************************************

!!

---

Reproducing locally

Verifying the current minimum setuptools version

The current build-system requirements were confirmed to be unusable by running the following commands:

python3.10 -m venv .venv-build
echo '*' > .venv-build/.gitignore
source .venv-build/bin/activate

python -m pip install --upgrade pip
python -m pip install build setuptools==40.8.0

python -m build --no-isolation

This results in a crash from within setuptools.

Testing setuptools v77.0.0

The build-system was updated and retested. (Note that "wheel" is no longer a recommended requirement, and that setuptools v77.0.0 was never actually published.)

python -m pip install setuptools==77.0.1
python -m build --no-isolation

The build succeeded.

Resolving build warnings

Finally, the latest version of setuptools was installed and all warnings were resolved.

python -m pip install --upgrade setuptools
python -m build --no-isolation

The following warnings were displayed:

• project.license as a TOML table is deprecated!!

  Please use a simple string containing a SPDX expression for project.license. You can also use project.license-files. (Both options available on setuptools>=77.0.0).

• License classifiers are deprecated.

  Please consider removing the following classifiers in favor of a SPDX license expression:

  License :: OSI Approved :: MIT License

Therefore, the license and classifiers in pyproject.toml were also updated.