Dsh Session Vacuum

`dsh-session-vacuum` is a DSH plugin designed to address slow loading and memory overflow issues caused by long session log bloat. By directly deleting unread streaming dead fragments on disk at startup, it reduces file sizes from the GB level to the MB level. The plugin features atomic replacement backups, a self-check mechanism, default enablement, and time-window protection. Because it has a destructive design, it is recommended to validate it first using `dryRun` mode. It only affects files on disk and does not impact the memory footprint of sessions that are already loaded.