dsh-geometric-mean: Geometric Mean Calculation Plugin

`dsh-geometric-mean` is a pure Node.js plugin for DeepSeek Harness (DSH) that addresses aggregation calculations for growth-rate or ratio-based data in model inference. It depends on `@deepseek-ai/cordis` and `@deepseek-ai/dsh-tools` and is open-sourced under the MIT License. Before use, ensure that the environment dependencies are met, and review the source code to confirm the calculation logic.