feat(tvix/store): add SledDirectoryService

Change-Id: I8e97a59da2c6623f4cca746efa741097a6dbe5b1
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7871
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

tvix/store/src/tests/mod.rs

@@ -1,6 +1,7 @@
 use crate::proto::{Directory, DirectoryNode, FileNode, SymlinkNode, ValidateDirectoryError};
 use lazy_static::lazy_static;
 
+mod directory_service;
 mod path_info_service;
 mod pathinfo;