feat: enhance dynamic tool management with notifications and enable/disable

Summary

Enhance the Python SDK's dynamic tool management capabilities to match the TypeScript SDK by adding:

1. Automatic tools/list_changed notifications when tools are added/removed
2. Tool enable/disable functionality (temporary hiding without removal)

Background

The Python SDK currently supports adding and removing tools dynamically (see #1322), but lacks two key features present in the TypeScript SDK:

1. List Changed Notifications

The TypeScript SDK automatically sends notifications/tools/list_changed when tools are modified. This allows clients to know when they should refresh their tool list.

Python SDK gap: Currently, when calling add_tool() or remove_tool(), clients are not notified of the change and may show stale tool lists.

2. Enable/Disable Tools

The TypeScript SDK provides enable() and disable() methods on tools:

const tool = server.tool("myTool", ..., async () => { ... });
tool.disable()  // Hides from list_tools, blocks calls
tool.enable()   // Re-enables the tool
tool.remove()   // Permanently removes

Benefits:

• Temporarily hide tools without losing registration
• Re-enable tools without re-registering
• Useful for permission-based or state-based tool visibility

Python SDK gap: Only permanent removal via remove_tool() is supported. No way to temporarily disable/re-enable tools.

References

• Related PR: #1322 (adds remove_tool method)
• TypeScript SDK Dynamic Servers: https://github.com/modelcontextprotocol/typescript-sdk#dynamic-servers
• MCP spec supports notifications/tools/list_changed

Start with the Python SDK entry points for add_tool(), remove_tool(), list_tools(), and tool invocation, then compare their behavior with the referenced TypeScript SDK dynamic-server implementation. Done means added and removed tools trigger tools/list_changed notifications, while disabled tools are hidden and blocked, can be re-enabled, and remain removable.