Add is_watch_enabled method to VFS and enhance prefetch cache tests

- Introduced `is_watch_enabled` method to check the status of automatic file watching in the VFS.
- Added a new test for prefetch cache to validate metadata retrieval and error handling for walked roots and external paths.
- Updated the `watch` method in `StdBackend` for cleaner logic.
- Enhanced the `dir_init` field in `PrefetchCache` to store resolved init-file information for directories, improving prefetch operations.

src/lib.rs

@@ -39,6 +39,6 @@ pub use snapshot::{
     InstanceContext, InstanceMetadata, InstanceSnapshot, InstanceWithMeta, InstanceWithMetaMut,
     RojoDescendants, RojoTree,
 };
-pub use snapshot_middleware::{snapshot_from_vfs, Middleware, ScriptType};
+pub use snapshot_middleware::{snapshot_from_vfs, Middleware, ScriptType, INIT_FILE_PRIORITY};
 pub use syncback::{syncback_loop, FsSnapshot, SyncbackData, SyncbackResult, SyncbackSnapshot};
 pub use web::interface as web_api;