[lib] Introduce NeynarClient.fetchFarcasterChannelsByIDs
Summary:
This lets up query Neynar's channel/bulk API.
It helps address ENG-9930.
Depends on D13979
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/D13980