[功能] 将 DevToys CLI 工具暴露为模型上下文协议 (MCP) 服务器

• Reuses the CLI tool model — tools are discovered through MEF exactly like DevToys.CLI (from a Plugins folder next to the executable, or via the EXTRAPLUGIN env var). No changes to the tool model itself.
• Schema generation — each ICommandLineTool becomes one MCP tool named devtoys_<command-name> (e.g. devtoys_base64), with a JSON input schema generated from its [CommandLineOption] properties. OneOf<...> options (e.g. "text or file path") are exposed as a string and parsed at invocation time.
• Invocation — tools/call binds arguments (mirroring the CLI binding, including OneOf), runs the tool, and returns its captured console output plus a structured { stdout, stderr, exitCode } payload. Non-zero exit codes mark the result as an error. Invocations are serialized because the tools write to the process-wide console.
• Build — DevToys.MCP is published per-RID by the Nuke build alongside the CLI, and registered in the Windows/macOS/Linux solutions.
• Tests — xUnit tests added to DevToys.UnitTests (schema generation, argument conversion, OneOf parsing, result formatting).
• Purely additive — no existing runtime code is modified (27 files, +2242 lines). It builds in Release with no warnings and all unit tests pass.
• ModelContextProtocol (Apache-2.0) is added to THIRD-PARTY-NOTICES.md.

Example MCP client configuration: