upgrade mlx

setup.py

@@ -35,8 +35,8 @@ extras_require = {
     "yapf==0.40.2",
   ],
   "apple_silicon": [
-    "mlx==0.20.0",
-    "mlx-lm==0.19.3",
+    "mlx==0.21.1",
+    "mlx-lm==0.20.4",
   ],
 }