[lib] Wait to finish all followed channels queries before querying for a specific one

Summary:
This will allow us to avoid spamming out requests for every channel on app start. Most of the channels (probably all channels in most cases) will be channels the user follows on Farcaster.

Depends on D13976

Test Plan: 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/D13977