DeepSeek Harness Plugin: dsh-llm-extra-retry

`lim12137/dsh-llm-extra-retry` is a DSH plugin designed to address the issue of being unable to retry when the upstream returns the `PI_AI_ERROR` error code. The plugin provides a separate policy for this specific error: after detecting the error, it automatically retries once after waiting 20 seconds, without affecting the built-in default retry mechanism. Users can integrate it into a DSH environment by modifying the configuration, and can adjust the retry duration or number of attempts as needed.