refactor(app.tsx): use constants instead of hard coded strings for better readablility (#1391)

don't use inline function as it will create a new refrence everytime

src/time_constants.ts

@@ -0,0 +1,4 @@
+// time in milliseconds
+export const FONT_LOAD_THRESHOLD = 1000;
+export const TAP_TWICE_TIMEOUT = 300;
+export const INITAL_SCENE_UPDATE_TIMEOUT = 5000;