Bump rmcp from 0.15.0 to 1.4.0 in /codex-rs

Bumps [rmcp](https://github.com/modelcontextprotocol/rust-sdk) from 0.15.0 to 1.4.0.
- [Release notes](https://github.com/modelcontextprotocol/rust-sdk/releases)
- [Changelog](https://github.com/modelcontextprotocol/rust-sdk/blob/main/release-plz.toml)
- [Commits](modelcontextprotocol/rust-sdk@rmcp-v0.15.0...rmcp-v1.4.0)

---
updated-dependencies:
- dependency-name: rmcp
  dependency-version: 1.4.0
  dependency-type: direct:production
...

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Author: dependabot[bot]