add fftshift and ifftshift fft helpers (#2135)

* add fftshift and ifftshift fft helpers

* address comments

* axes have to be iterable

* fix fp error in roll + add test

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Co-authored-by: Aashiq Dheeraj <aashiq@aashiq-mbp-m4.local>

python/tests/test_ops.py

@@ -2961,6 +2961,11 @@ class TestOps(mlx_tests.MLXTestCase):
             y2 = mx.roll(x, s, a)
             self.assertTrue(mx.array_equal(y1, y2).item())
 
+    def test_roll_errors(self):
+        x = mx.array([])
+        result = mx.roll(x, [0], [0])
+        self.assertTrue(mx.array_equal(result, x))
+
     def test_real_imag(self):
         x = mx.random.uniform(shape=(4, 4))
         out = mx.real(x)