refactor(tvix/store): Asyncify PathInfoService and DirectoryService

We've decided to asyncify all of the services to reduce some of the
pains going back and for between sync<->async. The end goal will be for
all the tvix-store internals to be async and then expose a sync
interface for things like tvix eval io.

Change-Id: I97c71f8db1d05a38bd8f625df5087d565705d52d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9369
Autosubmit: Connor Brewster <cbrewster@hey.com>
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

tvix/store/src/import.rs

@@ -72,6 +72,7 @@ async fn process_entry(
         // upload this directory
         directory_putter
             .put(directory)
+            .await
             .map_err(|e| Error::UploadDirectoryError(entry.path().to_path_buf(), e))?;
 
         return Ok(proto::node::Node::Directory(proto::DirectoryNode {