layout: add helper for cached/external values to centralize recomputation

src/api/admin/cluster.rs

@@ -240,7 +240,6 @@ pub async fn handle_update_cluster_layout(
 			.merge(&roles.update_mutator(node, layout::NodeRoleV(new_role)));
 	}
 
-	layout.update_hashes();
 	garage
 		.system
 		.layout_manager

src/api/k2v/index.rs

@@ -29,7 +29,7 @@ pub async fn handle_read_index(
 		.system
 		.cluster_layout()
 		.all_nongateway_nodes()
-		.into_owned();
+		.to_vec();
 
 	let (partition_keys, more, next_start) = read_range(
 		&garage.k2v.counter_table.table,