Implement paging state restoration on process recreation and show user explicit retry buttons on paging errors

[HeroBrine1st]

This PR resolves page refreshing if application is required to free some memory to system. Tested on whole process death, but this bug was seen partially, with some components in navigation stack having cached data and some not having.

Other changes:

• Implemented page dropping feature to save memory on very long scrolls
• Reduced page size from 500 to 100 due to upstream bug with LazyList index restoration via keyed items
• Refactored Pager and moved away from AndroidX Paging architecture, leading to unencouragement of Pager multi-usage.
• Removed automatic retry to not bomb API server with requests
• Added retry buttons where applicable

This PR is being tested.

[HeroBrine1st]

There are bugs that are apparently fixed by 92c7ddf:

• Going into post screen from posts screen and back (no info on timing) refreshes page. It is not complete cache loss as probably no request is made to the server (order:random returned the same posts in the same order, which is unlikely to happen)
• Scroll snapping in the same situation as above (without refresh) but probably page dropping is involved

Attempts to get those bugs reproduced after that commit are futile, despite fixing nothing as state restoration feature is not used in this case

And, of course, prepend scroll position reset, which is seen for one frame (and immediately restored after). I don't see any same-frame solutions without architectural changes, so I left it as is.

Otherwise, this PR is complete and advanced features like agressive post caching are now possible