Install setuptools explicitly for Python 3.12+ compatibility

distutils was removed from the stdlib in Python 3.12, and setuptools is
no longer bundled. Explicitly installing it fixes `python setup.py sdist`
on 3.12 and 3.13.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: derek73

.github/workflows/python-package.yml

@@ -27,7 +27,7 @@ jobs:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies
       run: |
-        python -m pip install --upgrade pip
+        python -m pip install --upgrade pip setuptools
         python -m pip install twine
         python -m pip install sphinx
         if [ -f dev-requirements.txt ]; then pip install -r dev-requirements.txt; fi