Modify InfiniteScroller to work with PostThreadComponent subscription

Followup to https://github.com/bitclout/frontend/pull/245. Address the following todo in `PostThreadComponent`:
```
// TODO: Cleanup - Update InfiniteScroller class to de-duplicate this logic
```

We should either:
(a) Figure out how we might extend `infinite-scroller.ts` to handle how `PostThreadComponent` fetches data with `subscribe`
(b) Remove the TODO and leave `PostThreadComponent` as is

Start by reading `infinite-scroller.ts` and `PostThreadComponent`, especially the TODO about de-duplicating logic and the component's `subscribe`-based data fetching. Determine whether InfiniteScroller can support that subscription pattern; done means either implementing that extension or removing the TODO while leaving PostThreadComponent unchanged.

Written by the indexing model from the issue text.