add setuptools_scm

Without this, *.h files are not automatically included in the sdist, so building from the sdist (e.g. using `python -m build`) fails

pyproject.toml

@@ -1,5 +1,5 @@
 [build-system]
-requires = ["setuptools>=69.0", "pybind11"]
+requires = ["setuptools>=69.0", "setuptools_scm>=8", "pybind11"]
 build-backend = "setuptools.build_meta"
 
 [project]