Add support for MCP servers in Agent Loop

[ZbutwialyPiernik]

Currently, all agent tools must be manually defined using AgentTool.fromFunction, requiring developers to write boilerplate code for each tool's name, description, schema, and execution logic.

This proposal is to add MCP server integration that would allow agents to automatically load tools from MCP-compliant servers (e.g., AgentConfig.fromMcpServer("stdio://my-mcp-server")) instead of manually defining each tool. The integration should support the full MCP specification including tool discovery, schema extraction, and dynamic execution of remote tools.