processRemoteNotification

Converts an incoming FCM message into a typed PushNotification.

Call this from FirebaseMessagingService.onMessageReceived when the message data contains the "PingOne" key. The resulting PushNotification provides PushNotification.getPushType, PushNotification.approveNotification, PushNotification.denyNotification, and PushNotification.isCancelAuthentication for the full push response lifecycle.

Returns Result.success(null) when the native SDK returns both nulls — this indicates the message was a "silent" (extra verification) PingOne MFA push and should be silently ignored by the caller.