refactor(tvix/*store): use DS: DirectoryService

We implement DirectoryService for Arc<DirectoryService> and
Box<DirectoryService>, this is sufficient.

Change-Id: I0a5a81cbc4782764406b5bca57f908ace6090737
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11586
Tested-by: BuildkiteCI
Reviewed-by: Connor Brewster <cbrewster@hey.com>

tvix/castore/src/import/archive.rs

@@ -84,7 +84,7 @@ pub async fn ingest_archive<BS, DS, R>(
 ) -> Result<Node, IngestionError<Error>>
 where
     BS: BlobService + Clone + 'static,
-    DS: AsRef<dyn DirectoryService>,
+    DS: DirectoryService,
     R: AsyncRead + Unpin,
 {
     // Since tarballs can have entries in any arbitrary order, we need to