Consolidate fileSize formatting logic

ts/util/formatFileSize.ts

@@ -0,0 +1,7 @@
+// Copyright 2024 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+import filesize from 'filesize';
+
+export function formatFileSize(size: number): string {
+  return filesize(size, { round: 0 });
+}