Implement the Soulseek chat-room server messages against soulfind's
wire format:
- MessageFactory builders: room-list request (64), join (14),
leave (15), say (13).
- Handlers parsing the server side: RoomList (64) names+counts,
JoinRoom (14) membership, SayChatroom (13), UserJoinedRoom (16),
UserLeftRoom (17), LeaveRoom (15).
- Surface everything to the client as a drained RoomEvent stream plus
a room-list snapshot; new Client API: request_room_list, join_room,
leave_room, say_in_room, room_list, take_room_events.
Unit tests cover each builder and handler; server-gated e2e tests
exercise message delivery and room listing against soulfind.