Preloading samples in the OS file cache in background is slowed down to avoid FPS drop when starting to play after a cold start.

Loading all samples from a SSD takes ~13 seconds, which is less than the script timeout (~15s) so it can be safely done during the loading screen.

Improve preloader to attempt to load all samples within 15 seconds during cold startup. If all samples can't be loaded (HDD), continue with the background preloading.