Function write_loop_with_config 

pub async fn write_loop_with_config(
    storage: Arc<dyn StoragePlugin>,
    registry: Arc<PvRegistry>,
    rx: Receiver<PvSample>,
    shutdown: Receiver<bool>,
    cfg: WriteLoopConfig,
)

Same as write_loop but accepts the full WriteLoopConfig.

Thin wrapper that runs a 1-shard sharded pool — kept on the public surface for tests and any direct callers. The actual work happens in run_sharded_write_pool.