The engine once ready (null before and after unmount); changing it re-renders
Live engine (no re-render needed; e.g. inside onReady or after whenReady)
Resolves with the engine, or null when unmounted first / create failed (also null
when called before the mount effect ran, e.g. from a parent's layout effect)
Last
create/ render error (CharturboInitErrorwithout WebGPU / WebGL2)