Restore contacts from backup

XXClient library

• Improve error handling in UdMultiLookupCallback.

xx-messenger example

• Improve backup restoration.
• Restore contacts.
• Add contact lookup feature.
• Display contact ids.
• Improve sending requests.
• Restore username from restored facts, not from restored params.

Examples/xx-messenger/Sources/ContactFeature/ContactFeature.swift

@@ -184,6 +184,7 @@ public let contactReducer = Reducer<ContactState, ContactAction, ContactEnvironm
 
   case .lookup(.didLookup(let xxContact)):
     state.xxContact = xxContact
+    state.lookup = nil
     return .none
 
   case .sendRequestTapped: