private boolean isOnnx(ExpressionNode node) {
        if ( ! (node instanceof ReferenceNode reference)) return false;
        return reference.getName().equals("onnx") || reference.getName().equals("onnxModel");
    }
Extract the feature used to evaluate the onnx model. e.g. onnx(name) and add
that as a bind target and argument. During evaluation, this will be evaluated before
the rest of the expression and the result is added to the context. Also extract the
inputs to the model and add them as bind targets and arguments.
model-evaluation/src/main/java/ai/vespa/models/evaluation/BindingExtractor.java