* 1. add a challenge in chapter 2 as challenge 9
2. add a check_challenge.py script to makesure a challenge actually has answer
3. add blank lines to the file README_CN.md to look better
* delete redundant function
* code style check
* code style check
* style checkout change
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Co-authored-by: DuskSwan <aquark@foxmail.com>
* add multi online support
* add readme and requirements.txt
* refactor code to llm and challenges and update readme
* handle llm exception and return empty str
* update error handling
* fix gradio version and add concurrency control
* remove concurrency_limit
* update reame
