Add a fast path (no iterator creation) for a common case for repeating deques of size 1

Lib/test/test_deque.py

@@ -654,6 +654,15 @@ class TestBasic(unittest.TestCase):
         self.assertNotEqual(id(d), id(e))
         self.assertEqual(list(d), list(e))
 
+        for i in range(5):
+            for maxlen in range(-1, 6):
+                s = [random.random() for j in range(i)]
+                d = deque(s) if maxlen == -1 else deque(s, maxlen)
+                e = d.copy()
+                self.assertEqual(d, e)
+                self.assertEqual(d.maxlen, e.maxlen)
+                self.assertTrue(all(x is y for x, y in zip(d, e)))
+
     def test_copy_method(self):
         mut = [10]
         d = deque([mut])