Introduce typed error classes with metadata

Summary

Replace generic exceptions with SDK-native error classes that include useful metadata like fault attribution, retryability, and HTTP details.

Problem

The SDK currently raises generic exceptions from various layers (httpx, anyio, task groups) with no context about:

• Whether the error is retryable
• Who is at fault (client, server, network, protocol violation)
• HTTP status codes and response bodies (often discarded)

This makes it hard for users to build robust error handling.

Goal

A hierarchy of typed errors like:

• McpError (base) with fault, is_retryable, http_status_code, response_body
• McpTransportError for connection/network issues
• McpProtocolError for invalid JSON-RPC responses
• McpAuthError for 401/403 responses

_{AI Disclaimer}

首先追踪 SDK 当前在哪些位置暴露来自 httpx、anyio 和任务组的通用异常。定义拟议 McpError 层次结构的范围和元数据要求，包括故障归因、可重试性、HTTP 状态码和响应正文。设计确定且受影响的错误路径始终暴露带类型的 SDK 原生错误，即表示完成。