Make finalization part of the stream

ts/util/finalStream.ts

@@ -0,0 +1,22 @@
+// Copyright 2024 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import { Transform } from 'node:stream';
+
+export function finalStream(finalizer: () => Promise<void> | void): Transform {
+  return new Transform({
+    transform(data, enc, callback) {
+      this.push(Buffer.from(data, enc));
+      callback();
+    },
+    async final(callback) {
+      try {
+        await finalizer();
+      } catch (error) {
+        callback(error);
+        return;
+      }
+      callback(null);
+    },
+  });
+}