dsh-euler-totient: Euler's Totient Function Plugin

The `dsh-euler-totient` plugin for DeepSeek Harness (DSH), maintained by uckkk, is intended to provide mathematical computation support for model inference. It is built with pure Node.js, has no network dependencies, and supports Euler's totient function calculations. To install, run `dsh plugin add github:uckkk/dsh-euler-totient`, then invoke the registered tool in a session to use it. Its dependencies include `@deepseek-ai/cordis` and `@deepseek-ai/dsh-tools`, and it is released under the MIT License.