【BUG】 socketio:clear 命令异常， 当 redis 配置了 prefix 选项后，一定会出现清除失败！

redis配置了前缀，并且 scan 配置了Redis::SCAN_PREFIX (其实配置不配置，都会出现问题，只要redis的options配置了前缀)

情况1：
当 scan 选项没有配置时，则scan默认为不加前缀，则调用 scan 命令获取不到keys，所以就没有清除的效果

情况2:
当 scan 选项配置为Redis::SCAN_PREFIX 时，则调用scan 命令能获取到keys， 但这些key是原始的key (添加了前缀)， 则调用 del 命令会失败 (因为del也会自动添加前缀，就导致添加了两次前缀).

Start by tracing the socketio:clear command and how its Redis scan and delete operations handle configured prefixes. Reproduce the issue with a Redis prefix, testing both the default scan behavior and Redis::SCAN_PREFIX. Done means the command finds and deletes the intended keys without applying the prefix twice.

Scritto dal modello di indicizzazione a partire dal testo della issue.