feat(tvix/store): eliminate generics in BlobStore

To construct various stores at runtime, we need to eliminate associated
types from the BlobService trait, and return Box<dyn …> instead of
specific types.

This also means we can't consume self in the close() method, so
everything we write to is put in an Option<>, and during the first close
we take from there.

Change-Id: Ia523b6ab2f2a5276f51cb5d17e81a5925bce69b6
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8647
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/store/src/bin/tvix-store.rs

@@ -6,6 +6,7 @@ use std::path::Path;
 use std::path::PathBuf;
 use std::sync::Arc;
 use tracing_subscriber::prelude::*;
+use tvix_store::blobservice::BlobService;
 use tvix_store::blobservice::GRPCBlobService;
 use tvix_store::blobservice::SledBlobService;
 use tvix_store::directoryservice::GRPCDirectoryService;
@@ -112,14 +113,14 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
             let mut server = Server::builder();
 
             let nar_calculation_service = NonCachingNARCalculationService::new(
-                blob_service.clone(),
+                Box::new(blob_service.clone()),
                 directory_service.clone(),
             );
 
             #[allow(unused_mut)]
             let mut router = server
                 .add_service(BlobServiceServer::new(GRPCBlobServiceWrapper::from(
-                    blob_service,
+                    Box::new(blob_service) as Box<dyn BlobService>,
                 )))
                 .add_service(DirectoryServiceServer::new(
                     GRPCDirectoryServiceWrapper::from(directory_service),
@@ -156,7 +157,7 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
                 GRPCNARCalculationService::from_client(path_info_service_client);
 
             let io = Arc::new(TvixStoreIO::new(
-                blob_service,
+                Box::new(blob_service),
                 directory_service,
                 path_info_service,
                 nar_calculation_service,