src/transformers/onnx/config.py/OnnxConfigWithPast/_flatten_past_key_values_
class OnnxConfigWithPast:    def _flatten_past_key_values_(self, flattened_output, name, idx, t):
        flattened_output[f"{name}.{idx}.key"] = t[0]
        flattened_output[f"{name}.{idx}.value"] = t[1]