[lib] Don't query Neynar for Farcaster channel avatars if unused
Summary:
This eliminates most fetches, since we mostly aren't using Farcaster channel avatars yet.
Depends on D13982
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/D13983