[lib] Extract user ids from server socket messages

Summary:
issue: ENG-7742
This handler extracts user ids from server messages that come over the socket.

Test Plan:
Sent a message from user1 and checked that updates/server messages on user2 are parsed correctly - correct user ids are extracted.
Tested that no errors show up

Reviewers: tomek, kamil

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D12052