Messenger - restore from backup

XXMessengerClient

• Add MessengerRestoreBackup function wrapper
  • Restore CMix and UserDiscovery from backup
  • Return restored params and contacts
• Add MessengerIsListeningForMessages function

xx-messenger example

• Restore backup from file
• Refactor app startup

Sources/XXMessengerClient/Utils/BackupParams.swift

+import Foundation
+
+public struct BackupParams: Equatable, Codable {
+  public init(
+    username: String,
+    email: String?,
+    phone: String?
+  ) {
+    self.username = username
+    self.email = email
+    self.phone = phone
+  }
+
+  public var username: String
+  public var email: String?
+  public var phone: String?
+}