Fix leak for multi-output primitives which are never detached (#1059)

* fix multi output leak

* ignore arrays that will be detached

* add some comments

* stray print

python/tests/test_array.py

@@ -1694,6 +1694,22 @@ class TestArray(mlx_tests.MLXTestCase):
         b = pickle.loads(pickle.dumps(a))
         self.assertTrue(mx.array_equal(mx.array(a), mx.array(b)))
 
+    @unittest.skipIf(not mx.metal.is_available(), "Metal is not available")
+    def test_multi_output_leak(self):
+        def fun():
+            a = mx.zeros((2**20))
+            mx.eval(a)
+            b, c = mx.divmod(a, a)
+            del b, c
+
+        fun()
+        mx.synchronize()
+        peak_1 = mx.metal.get_peak_memory()
+        fun()
+        mx.synchronize()
+        peak_2 = mx.metal.get_peak_memory()
+        self.assertEqual(peak_1, peak_2)
+
 
 if __name__ == "__main__":
     unittest.main()