Update ADK doc according to issue #1256 - 4 - McpToolset Progress Updates

[adk-bot]

4. Summary of the change

Doc file: docs/tools-custom/mcp-tools.md

Current state:

48:
49: The following examples demonstrate how to use McpToolset within the adk web development environment. For scenarios where you need more fine-grained control over the MCP connection lifecycle or are not using adk web, refer to the "Using MCP Tools in your own Agent out of adk web" section later in this page.
50:
51: ### Example 1: File System MCP Server

Proposed Change:

48:
49: The following examples demonstrate how to use McpToolset within the adk web development environment. For scenarios where you need more fine-grained control over the MCP connection lifecycle or are not using adk web, refer to the "Using MCP Tools in your own Agent out of adk web" section later in this page.
50:
51: ### Handling Progress Updates
52:
53: For long-running tools, McpToolset supports a progress_callback. This allows you to receive real-time updates from the MCP server. You can provide a simple callback function or a factory that creates callbacks with access to the runtime context (e.g., to update session state).
54:
55: python 56: async def my_progress_callback(progress: float, total: float, message: str): 57: print(f"Progress: {progress}/{total} - {message}") 58: 59: toolset = McpToolset( 60: connection_params=..., 61: progress_callback=my_progress_callback 62: ) 63:
64:
65: ### Example 1: File System MCP Server

Reasoning:
The McpToolset and McpTool classes now support a progress_callback parameter for handling progress notifications from MCP servers. This is useful for long-running operations.

Reference: src/google/adk/tools/mcp_tool/mcp_toolset.py