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}

Comece rastreando onde o SDK atualmente expõe exceções genéricas de httpx, anyio e grupos de tarefas. Defina o escopo e os requisitos de metadados para a hierarquia McpError proposta, incluindo atribuição da falha, possibilidade de novas tentativas, códigos de status HTTP e corpos das respostas. Considera-se concluído quando o design estiver resolvido e os caminhos de erro afetados expuserem consistentemente erros tipados nativos do SDK.