Function spawn_worker 

pub fn spawn_worker(
    index: Arc<InMemoryMetadataIndex>,
    slatedb: Option<Arc<SlateDbMetadataIndex>>,
    deleter: Arc<dyn EvictionDeleter>,
    config: LruConfig,
    emit: EvictionEmit,
) -> LruEvictionWorker

Spawn the eviction worker. The returned worker holds the join handle and signals stop on drop. Returns immediately; the loop runs on the spawned thread.