[RFC] Support dry-run mode | 限流和熔断空跑问题

现在想在正式启用限流功能前，空跑限流功能，关于限流后能我们这边定义了错误码返回，现在只想看到真正被限流后错误码返回，但不想真正的进行限流，请问目前sentinel支持该功能吗？

Review Sentinel’s existing rate-limiting and circuit-breaking behavior and documentation first, focusing on how blocked requests and configured error codes are currently handled. Define the dry-run semantics, affected components, configuration entry points, and tests needed to verify that decisions are reported without enforcing limits.

Written by the indexing model from the issue text.