pub trait State: Send + Sync {
// Provided methods
fn on_enter(&mut self, _universe: &mut Universe) { ... }
fn on_exit(&mut self, _universe: &mut Universe) { ... }
fn on_pause(&mut self, _universe: &mut Universe) { ... }
fn on_resume(&mut self, _universe: &mut Universe) { ... }
fn on_process(&mut self, _universe: &mut Universe) -> StateChange { ... }
fn on_process_background(&mut self, _universe: &mut Universe) { ... }
}