[lib][native][web] Introduce FarcasterChannelPrefetchHandler
Summary:
This handler will make sure that we fetch all non-followed channel info in bulk, thereby reducing the total number of Neynar queries on app start.
Depends on D13981
Test Plan:
- In combination with other diffs, tested that channel avatars still load on both web and native
- Tested on both native and web by logging each NeynarClient query and seeing which ones get triggered
Reviewers: varun, will
Reviewed By: will
Subscribers: tomek
Differential Revision: https://phab.comm.dev/D13982