bug/66552 unload (lazy) activity tab pages when they are outside viewport after for more than 3s excluding the first and last pages

[akabiru]

https://community.openproject.org/wp/66552

Attempt to eliminate scroll repaint delays by having less DOM nodes at any given time.

Skeleton (lazy-page controller) → turbo:stream replace → Loaded content (unloadable-page controller)

                ↓                                                                       ↓
    appear(): load content                                       disappear(): unload to skeleton
    disappear(): cancel load