Backup improvements & example

XXMessengerClient library

• Fix race condition issues when starting the backup and setting initial parameters.
• Add BackupStorage utility that can store the backup.
• Store BackupStorage.Backup on disk.

xx-messenger example

• Start backup
• Resume backup
• Stop backup
• Store backups in storage
• Observe backup storage
• Export backup from storage
• Resume backup on launch

Examples/xx-messenger/Sources/AppFeature/AppEnvironment+Live.swift

@@ -28,7 +28,7 @@ extension AppEnvironment {
       handleConfirm: .live(db: dbManager.getDB),
       handleReset: .live(db: dbManager.getDB)
     )
-    let backupStorage = BackupStorage.live(now: Date.init)
+    let backupStorage = BackupStorage.onDisk()
     let mainQueue = DispatchQueue.main.eraseToAnyScheduler()
     let bgQueue = DispatchQueue.global(qos: .background).eraseToAnyScheduler()