[Perf: App Start Warm] Reduce splash screen animation time

[Julesssss]

The native splash screen hider (SplashScreenHider/index.native.tsx) runs a 250ms opacity fade + 200ms scale animation after the app is ready. This is dead time added to every warm start measurement and user-perceived startup.

Reducing the animation duration is a low-risk way to shave time off both the metric and the user experience.

[Julesssss]

Tested shorter animations here but it didn't look good. Closed and moving onto a native animation test, that would reduce load on JS bridge but keep same animation.