Add compatibility with React 19 <Activity />

[shacha086]

Describe the feature you'd love to see
React 19 introduces the new component which allows parts of the tree to be paused or hidden without unmounting, so component state, refs, and DOM can be retained across visibility or activity changes
(see docs: https://react.dev/reference/react/Activity)

This feature would be very helpful for managing certain states more conveniently. I would be grateful if this could be considered!

[shacha086]

Alternatively, is there any way to keep the real DOM element after unmounting?

[JoviDeCroock]

Our current Suspense could already enable functionality like this because that's how our resumed hydration works. You can use something like https://stackblitz.com/edit/vitejs-vite-oqisjfl9?file=src%2FSuspenseTransition.tsx to do that. Not sure if this fully satisfies Activity yet but worth mentioning