Improve exception tracebacks for easier debugging

Summary

Make exception tracebacks clearer and easier to understand by reducing asyncio/anyio wrapper noise.

Problem

• Exceptions are often wrapped in multiple layers of asyncio/anyio task group machinery
• Tracebacks are hard to read and don't clearly point to the root cause
• The raise_exception flag is not consistently respected
• Errors from deep inside task groups obscure the actual failure point

Goal

• Cleaner tracebacks that point to user code, not SDK internals
• Raise exceptions from the main context where possible
• Reduce nesting of exception wrappers

Related

• #743 - RuntimeError but the actual root cause is not logged correctly
• #396 - MCP Server: Inconsistent Exception Handling in @app.call_tool
• #1401 - ClientSession Error Handling
• #1742 - Introduce typed error classes with metadata

_{AI Disclaimer}

Nenhum arquivo ou teste é identificado na issue. Comece rastreando os caminhos dos grupos de tarefas de asyncio/anyio e todo uso do sinalizador raise_exception; depois, revise as issues vinculadas sobre tratamento de exceções. O trabalho estará concluído quando os tracebacks expuserem a falha no nível do usuário, o aninhamento de wrappers for reduzido e raise_exception for respeitado de forma consistente.