Add compatibility with React 19 <Activity />

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!