Render and cache notes in the background before playing

[LucasCTN]

After testing UTSU, I noticed that notes only start rendering once you click the play button. After that, it is cached.

Ideally, the notes should be rendered and cached on background once the mouse click is released, to make user waiting time shorter.

Reading the code, it seems that the function render from Engine.java would be used to render (and cache) each region of notes that is not currently being interacted with?