[lib] Close tunnelbroker socket when app is in background

Summary:
This diff closes tunnelbroker socket when app goes to background in order to prevent messages from decrypting twice and weird socket state.

https://linear.app/comm/issue/ENG-9741/tunnelbroker-socket-onmessage-is-triggered-before-re-opening-socket

Test Plan:

1. Run the app
2. Put the app in the background
3. Send some DMs to the app
4. Bring the app to the foreground
5. Observe in logs that the socket is closed after going to the background and verify that no message is received before closing the socket

Reviewers: tomek, kamil

Reviewed By: kamil

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D13787