[amarose]

Problem

When a push cold-starts the app, onMessageReceived returned before the notification
was built. Firebase then destroyed the messaging service and
PushNotificationDelegate.onDestroy() cancelled the in-flight image download:

• since 3.2.1 the notification was dropped entirely (JobCancellationException, no notify()),
• when the download failed first (network still blocked right after a cold start),
  the notification was posted without its image.

Fix

• onMessageReceived waits on the messaging worker thread until the notification is posted;
  calls from the main thread keep the async path to avoid ANRs
• onDestroy() no longer cancels in-flight work
• image/icon downloads retry network errors with backoff within a shared 8 s budget;
  any other failure posts the notification without the image
• CancellationException is no longer swallowed

No public API changes (apiCheck passes), so integrations forwarding messages through
FcmMessagingServiceDelegate get the fix by bumping the version.

Tests

PushNotificationDelegateTest: service destroyed mid download, transient network error,
non-retryable error. The first two fail without the fix and pass with it.