Product updates: L40Ss, proxy auth tokens, and sandbox disk snapshotting

Introduced a Filesystem API for reading and writing files within Sandboxes, and disk snapshotting capabilities for Sandboxes. Disk snapshotting allows for creating snapshots of the entire Sandbox state, branching from snapshots, and restoring from snapshots to eliminate cold-start times. Also added `fsnotify-like` file watching and support for larger write payloads (up to 1 GiB) to Sandboxes.