Include zig build in the build process.

pyproject.toml

@@ -1,6 +1,7 @@
 [build-system]
 requires = ["setuptools>=61.0", "cffi>=2.0.0"]
-build-backend = "setuptools.build_meta"
+build-backend = "build_backend"
+backend-path = ["."]
 
 [project]
 name = "pyaegis"
@@ -25,6 +26,7 @@ Homepage = "https://github.com/aegis-aead/libaegis"
 [dependency-groups]
 dev = [
     "pytest>=8.4.2",
+    "setuptools>=80.9.0",
 ]
 
 [tool.setuptools]