feat(tvix/store): implement PathInfoService with sled

This uses [sled](https://github.com/spacejam/sled) to store PathInfo
objects.

Change-Id: I12e8032e5562af8f884efa23a78049fd1108fdbc
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7726
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 path_info_service;
 mod pathinfo;
 
 lazy_static! {