Activations LeakyReLU / PReLU / Softplus / Mish (#109)

* Leaky_relu / prelu / softplus / mish

* added tests

* updated bench

* remove torch refs, add init to PReLU

* added arvix reference to mish

* added missing docs

python/tests/mlx_tests.py

@@ -2,8 +2,10 @@
 
 import os
 import unittest
+from typing import Callable, List, Tuple
 
 import mlx.core as mx
+import numpy as np
 
 
 class MLXTestCase(unittest.TestCase):
@@ -16,3 +18,16 @@ class MLXTestCase(unittest.TestCase):
 
     def tearDown(self):
         mx.set_default_device(self.default)
+
+    def assertEqualArray(
+        self,
+        args: List[mx.array | float | int],
+        mlx_func: Callable[..., mx.array],
+        expected: mx.array,
+        atol=1e-2,
+        rtol=1e-2,
+    ):
+        mx_res = mlx_func(*args)
+        assert tuple(mx_res.shape) == tuple(expected.shape), "shape mismatch"
+        assert mx_res.dtype == expected.dtype, "dtype mismatch"
+        np.testing.assert_allclose(mx_res, expected, rtol=rtol, atol=atol)