Function revalidate_buckets 

async fn revalidate_buckets(
    profile_id: ProfileId,
    _profile: Profile,
    default_region: String,
    pool: Arc<ClientPool>,
    cache: CacheHandle,
    log: Arc<RwLock<NotificationLog>>,
    channel: AppHandle,
)

Re-fetch the bucket list and update the cache + emit events. Called from the background task spawned on a stale cache hit.