Require cython in the build-system

pyproject.toml

@@ -0,0 +1,6 @@
+[build-system]
+requires = [
+  "Cython >= 0.20",
+  "setuptools >= 58.3",
+]
+build-backend = "setuptools.build_meta"

setup.py

@@ -81,9 +81,7 @@ setup(
     author_email="jackrobison@lbry.com",
     url="https://github.com/lbryio/lbry-rocksdb",
     license='BSD License',
-	python_requires=">=3.7.0",
-    setup_requires=['setuptools>=25', 'Cython>=0.20'],
-    install_requires=['setuptools>=25'],
+    python_requires=">=3.7.0",
     package_dir={'rocksdb': 'rocksdb'},
     packages=find_packages('.'),
     ext_modules=cythonize([Extension(