fix(caching): properly respect ttl for all cache levels

ts/levelcache.classes.cacheentry.ts

@@ -29,6 +29,9 @@ export class CacheEntry
   @plugins.smartjson.foldDec()
   contents: Buffer;
 
+  @plugins.smartjson.foldDec()
+  public createdAt: number;
+
   public toStorageJsonString(): string {
     return this.foldToJson();
   }