Runtime cache CLI commands

A new once cache CLI lets you interact with the runtime cache directly. You can hash files and directories with cache hash, store and fetch content-addressed blobs with cache blob put/get/exists, and read, write, or delete action results with cache action get/put/forget. cache action get also supports --if-success so a script can skip re-running when the cached result is a successful one. This gives scripts a way to implement skip-if-unchanged and restore-instead-of-regenerate workflows without relying on annotated script targets.