getDeviceId method
Retrieves a unique identifier for the device.
On Android, this attempts to use a hardware-backed Widevine DRM ID,
falling back to the Android ID (device_info_plus) if unavailable.
On iOS, this generates a unique UUID or uses the vendor ID, and securely
persists it in the iOS Keychain across app reinstalls.
Returns a Future<String?> containing the device ID, prefixed with
either android_ or ios_.
Implementation
Future<String?> getDeviceId() {
return DeviceSecurityPlatform.instance.getDeviceId();
}