refactor(tvix/store): use Arc instead of Box

This allows us to blob services without closing them before putting them
in a box.
We currently need to use Arc<_>, not Rc<_>, because the GRPC wrappers
require Sync.

Change-Id: I679c5f06b62304f5b0456cfefe25a0a881de7c84
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8738
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI
Autosubmit: flokli <flokli@flokli.de>

tvix/store/src/proto/grpc_directoryservice_wrapper.rs

@@ -8,13 +8,13 @@ use tonic::{async_trait, Request, Response, Status, Streaming};
 use tracing::{debug, instrument, warn};
 
 pub struct GRPCDirectoryServiceWrapper {
-    directory_service: Arc<Box<dyn DirectoryService>>,
+    directory_service: Arc<dyn DirectoryService>,
 }
 
-impl From<Box<dyn DirectoryService>> for GRPCDirectoryServiceWrapper {
-    fn from(value: Box<dyn DirectoryService>) -> Self {
+impl From<Arc<dyn DirectoryService>> for GRPCDirectoryServiceWrapper {
+    fn from(value: Arc<dyn DirectoryService>) -> Self {
         Self {
-            directory_service: Arc::new(value),
+            directory_service: value,
         }
     }
 }