feat(py):add mcp plugin and relevant tests

[MengqinShen]

This big changes aims to add mcp plugin to mirror all the functionalities in js/plugins/mcp in JS SDK.
CHANGELOG:

1. Added a plugin to enable Genkit applications to interact with the Model Context Protocol, allowing them to function as both clients and servers.
2. Added a 'resource' action kind to Genkit, enabling the definition and management of URI-addressable content
3. MCP Client Implementation: Provided a client that can connect to external MCP servers, list their tools, prompts, and resources, and execute them within a Genkit application.
4. MCP Server Implementation: Developed a server that exposes Genkit's registered tools, prompts, and resources to external MCP clients, facilitating interoperability.
5. Included extensive unit and integration tests for the MCP plugin, covering client-server communication, resource handling, and conversion utilities.

[gemini-code-assist]

Summary of Changes

Hello @MengqinShen, 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 integrates the Model Context Protocol (MCP) into the Python Genkit SDK, significantly enhancing its interoperability capabilities. It introduces a new 'resource' action type, allowing developers to define and manage content accessible via URIs. The new MCP plugin provides both client and server functionalities, enabling Genkit applications to consume services from other MCP-compliant systems and expose their own tools, prompts, and resources. This lays the groundwork for a more connected and extensible Genkit ecosystem.

Highlights

• Model Context Protocol (MCP) Plugin: Introduced a new Python plugin to enable Genkit applications to interact with the Model Context Protocol, allowing them to function as both clients and servers.
• New Resource Action Type: Added a 'resource' action kind to Genkit, enabling the definition and management of URI-addressable content, which can be accessed via fixed URIs or URI templates.
• MCP Client Implementation: Provided a client that can connect to external MCP servers, list their tools, prompts, and resources, and execute them within a Genkit application.
• MCP Server Implementation: Developed a server that exposes Genkit's registered tools, prompts, and resources to external MCP clients, facilitating interoperability.
• Enhanced Prompt Definition: Modified the 'define_prompt' function to allow explicit naming of prompts, enabling their registration as discoverable actions for MCP and Dev UI.
• Comprehensive Testing: Included extensive unit and integration tests for the MCP plugin, covering client-server communication, resource handling, and conversion utilities.

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[gemini-code-assist]

Code Review

This pull request introduces a significant new feature, the MCP plugin for Python, along with comprehensive examples and tests. The overall structure and implementation are well-done. I've identified a critical bug related to an undefined function that will prevent the server from working, as well as several opportunities for improvement in terms of code efficiency, clarity, and robustness. My comments focus on addressing these points to enhance the quality of the new plugin.