Add support for 'scroll up refresh' in the gallery.

src/utils/basic.ts

@@ -191,3 +191,8 @@ export const isSuperset = (superset: Set<unknown>, subset: Set<unknown>) => {
   }
   return true;
 };
+
+// Usage of this function needs to be justified with a comment.
+export const sleep = async (seconds: number) => {
+  await new Promise((r) => setTimeout(r, seconds * 1000));
+};