Create an iterator of tensors from node attributes of an ONNX model.

def _get_attribute_tensors(onnx_model_proto):  # type: (ModelProto) -> Iterable[TensorProto]
    """Create an iterator of tensors from node attributes of an ONNX model."""
    for node in onnx_model_proto.graph.node:
        for attribute in node.attribute:
            if attribute.HasField("t"):
                yield attribute.t
            for tensor in attribute.tensors:
                yield tensor