perf: add O_DIRECT uploads and stabilize RPC continuation shutdown

Implements DirectIoFile for faster package uploads by bypassing page cache.
Refactors RpcContinuations to support graceful WebSocket shutdown via
broadcast signal, improving stability during daemon restart.

core/src/context/rpc.rs

@@ -62,8 +62,8 @@ pub struct RpcContextSeed {
     pub db: TypedPatchDb<Database>,
     pub sync_db: watch::Sender<u64>,
     pub account: SyncRwLock<AccountInfo>,
-    pub net_controller: Arc<NetController>,
     pub os_net_service: NetService,
+    pub net_controller: Arc<NetController>,
     pub s9pk_arch: Option<&'static str>,
     pub services: ServiceMap,
     pub cancellable_installs: SyncMutex<BTreeMap<PackageId, oneshot::Sender<()>>>,
@@ -346,10 +346,10 @@ impl RpcContext {
             services,
             cancellable_installs: SyncMutex::new(BTreeMap::new()),
             metrics_cache,
+            rpc_continuations: RpcContinuations::new(Some(shutdown.clone())),
             shutdown,
             lxc_manager: Arc::new(LxcManager::new()),
             open_authed_continuations: OpenAuthedContinuations::new(),
-            rpc_continuations: RpcContinuations::new(),
             wifi_manager: Arc::new(RwLock::new(wifi_interface.clone().map(|i| WpaCli::init(i)))),
             current_secret: Arc::new(
                 Jwk::generate_ec_key(josekit::jwk::alg::ec::EcCurve::P256).map_err(|e| {