class_docstr: This prompt version follows the Llama2-chat's prompt format:
  ```
  <s>[INST] <<SYS>>
  {{ system_prompt }}
  <</SYS>>
  
  {{ user_msg_1 }} [/INST] {{ model_answer_1 }} </s><s>[INST] {{ user_msg_2 }} [/INST]
  ```
  reference: https://huggingface.co/blog/llama2#how-to-prompt-llama-2
code: def preprocess_ctx(self, ctx, max_length):
      return super().preprocess_ctx(
          ctx,
          max_length,
          ctx_prompt=f"{self.INSTRUCTION}\n\n",
          summary_prompt=" [/INST] ",
      )
  
imports: import os
  import inspect
  from lm_eval.utils import rouge2_mecab
  from lm_eval.base import rf, Task
label_desc: Use image node_id 2 for calling the XLSumJaWithLlama2 obj's underlying member method code with example usage: obj.preprocess_ctx(ctx, max_length) and returns: super