dsh-latency-pct: Latency Percentile Plugin

DeepSeek Harness (DSH) introduces the `dsh-latency-pct` plugin, designed to address the challenge of accurately assessing response quality in model inference development using average latency alone. Maintained by uckkk and implemented in pure Node.js, the plugin has no network dependencies and runs locally. Its core features include precise latency percentile calculation and detailed result output. Once installed via command and required dependencies are satisfied, users can invoke it in DSH sessions to quantitatively analyze the distribution of inference latency.