Synchronous backups

[Jasonvdb]

Enables apps using react-native-ldk to securely persist node state remotely and restore it using a seed. Backups now happen synchronously in the native code instead of unreliable async RN events to trigger backups.

Clients in Swift, Kotlin, and NodeJS (for testing).

See server readme for details on setting up and how it works.

Testing:

Once server is setup update constants.ts in the example app with the server details.

Server test: npm run test

App test: Try restore from server button in example app.

[coreyphillips]

After performing the following steps in the example app.

1. Tap "Create New Account"
2. Tap "Backup self check"

The following error is received:

LOG  react-native-ldk: Error: Failed to decrypt backup payload. The operation couldn’t be completed. (CryptoKit.CryptoKitError error 3.).
Message: 'Failed to decrypt backup payload. The operation couldn’t be completed. (CryptoKit.CryptoKitError error 3.)'
ERROR  Backup check failed [Error: Failed to decrypt backup payload. The operation couldn’t be completed. (CryptoKit.CryptoKitError error 3.)]

[Jasonvdb]

Nice find thanks @coreyphillips. It was the cached bearer token from the previous wallet that just needed to be cleared here.

When creating the new wallet the backup client still had the bearer token from the previous wallet and if that didn't expire it tried to use that token to restore the wrong file but couldn't decrypt it because wallet's seed changed.