feat: add mcp middleware hook

[JasmineLCY]

Checklist

• npm test passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

Description of change

[gemini-code-assist]

Summary of Changes

Hello @JasmineLCY, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a new feature that provides extensible middleware hooks for the MCP (Micro-Controller-Proxy) system. It allows developers to inject custom logic to be executed both before and after the core MCP middleware processing, enhancing control and observability over request flows within the application.

Highlights

• New Middleware Hooks: Introduced middlewareStart and middlewareEnd optional hooks to the MCPControllerHook interface, allowing custom logic to be executed before and after MCP controller middleware processing.
• Middleware Hook Execution: Implemented the execution of these new middlewareStart and middlewareEnd hooks within the mcp_body_middleware when ctx.app.config.mcp.hooks are defined.
• Configuration and Logging: Added configuration for custom loggers (mcpMiddewareStartLogger and mcpMiddewareEndLogger) in test fixtures to track the execution of the new middleware hooks.
• Test Coverage: Updated existing test cases to include assertions that verify the proper functioning and logging of the newly introduced middleware hooks, ensuring their correct integration.

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[gemini-code-assist]

Code Review

This pull request introduces a middleware hook mechanism for MCP, allowing custom logic to be executed at the start and end of MCP middleware processing. The changes include defining the hook interface, integrating it into the MCP middleware, and passing the hooks via the application configuration. The implementation is sound and is accompanied by tests. I have a couple of suggestions to improve the robustness of the test hook implementation and reduce code duplication in the tests.

[killagu]

LGTM