Function spawn_sync_loop 

pub fn spawn_sync_loop<C, O>(
    engine: Arc<CdcSyncEngine<C, O>>,
    interval: Duration,
    cancel: CancellationToken,
    ddl_lock: Arc<RwLock<()>>,
) -> JoinHandle<()>
where
    C: CdcConsumer + Send + Sync + 'static,
    O: OlapEngine + Send + Sync + 'static,

Spawn a background task that continuously polls CDC and syncs to OLAP.

The loop runs sync_once() on the given interval, logging results and errors. It shuts down gracefully when the CancellationToken is cancelled.

The ddl_lock is acquired as a read lock before each cycle to prevent interleaving with schema changes (which take a write lock).

Returns

A JoinHandle for the background task. The caller retains the CancellationToken and is responsible for cancelling it to stop the loop.