dsh-iso8601: ISO8601 Time Format Conversion Tool

The DSH plugin `dsh-iso8601` is designed for time format conversion in agent development, supporting the conversion of various time formats to the ISO 8601 standard. Implemented in Node.js, it operates without network dependencies. The installation command is `dsh plugin add github:uckkk/dsh-iso8601`, and upon installation, the relevant tools can be invoked directly within a session. Before use, the dependencies on `@deepseek-ai/cordis` (^4.0.1) and `@deepseek-ai/dsh-tools` (>=0.1.0-rc.6) must be satisfied.