feat(gif preview): add utils functions

src/services/util.js

@@ -1,3 +1,17 @@
+export function delay(duration) {
+  return new Promise((resolve, _) => {
+    setTimeout(() => {
+      resolve()
+    }, duration)
+  })
+}
+
+export function* cycle(xs) {
+  while (true) {
+      yield* xs
+  }
+}
+
 export function calcProgress (from, to, value) {
   return from + ((to - from) * value)
 }