xp2{tensorflow,torch}: convert NumPy arrays using dlpack (#686)

* xp2{tensorflow,torch}: convert NumPy arrays using dlpack

Newer versions of NumPy can expose arrays as dlpack capsules. Use this
functionality (when supported) to speed up NumPy -> Torch/Tensorflow
array conversion.

* Fix up copy paste error

Author: danieldk

thinc/util.py

@@ -314,6 +314,8 @@ def xp2torch(
     if hasattr(xp_tensor, "toDlpack"):
         dlpack_tensor = xp_tensor.toDlpack()  # type: ignore
         torch_tensor = torch.utils.dlpack.from_dlpack(dlpack_tensor)
+    elif hasattr(xp_tensor, "__dlpack__"):
+        torch_tensor = torch.utils.dlpack.from_dlpack(xp_tensor)
     else:
         torch_tensor = torch.from_numpy(xp_tensor)
     if requires_grad:
@@ -350,6 +352,8 @@ def xp2tensorflow(
     if hasattr(xp_tensor, "toDlpack"):
         dlpack_tensor = xp_tensor.toDlpack()  # type: ignore
         tf_tensor = tf.experimental.dlpack.from_dlpack(dlpack_tensor)
+    elif hasattr(xp_tensor, "__dlpack__"):
+        tf_tensor = tf.experimental.dlpack.from_dlpack(xp_tensor)
     else:
         tf_tensor = tf.convert_to_tensor(xp_tensor)
     if as_variable: