[关闭特定错误码的熔断逻辑] 希望避免 EINVAL 触发熔断

目前当下游返回 EINVAL 错误码时会触发熔断，但 EINVAL 是比较常见的错误码，能否有办法去避免这个错误码触发熔断。

The issue names no files, tests, or entry points. Start by locating brpc's circuit-breaker handling and how downstream error codes are classified; clarify whether EINVAL should be configurable or always excluded, then verify that the chosen behavior prevents EINVAL from tripping the breaker without changing other error handling.

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