Replace nearby api with actual BLE library

[dergoegge]

BLE stuff for iOS:
?

BLE stuff for android:
https://developer.android.com/guide/topics/connectivity/bluetooth-le
https://developer.android.com/reference/android/bluetooth/BluetoothGattServer

Creating background tasks in react native to handle BLE events:
https://reactnative.dev/docs/headless-js-android