feat: store image metadata in sqlite and images on disk

lib/promise.ts

@@ -87,7 +87,7 @@ export class ConcurrentPromiseQueue {
    */
   private queues: PromiseQueue[] = [];
 
-  constructor(concurrency: number) {
+  constructor(concurrency: number = 1) {
     this.queues = Array.from({ length: concurrency }).map(() => {
       return new PromiseQueue();
     });