fix(python): Use setuptools.build_meta instead of legacy backend

The legacy backend (setuptools.backends._legacy:_Backend) was removed in
setuptools 70+. Use the modern setuptools.build_meta instead.

Author: Das-rebel

python/pyproject.toml

@@ -1,6 +1,6 @@
 [build-system]
-requires = ["setuptools>=64", "wheel"]
-build-backend = "setuptools.backends._legacy:_Backend"
+requires = ["setuptools>=61.0", "wheel"]
+build-backend = "setuptools.build_meta"
 
 [project]
 name = "a3m-router"