- Add SubscriberService struct with Database and Config dependencies
- Add NewSubscriberService constructor
- Add CreateSubscriber with IMSI allocation, auth key generation, and eSIM provisioning support
- Add GetSubscriber and GetSubscriberByIMSI for subscriber retrieval
- Add UpdateSubscriber for subscriber information updates
- Add SuspendSubscriber with session termination
- Add TerminateSubscriber with session termination and eSIM profile deactivation
- Add ListSubscribers with pagination and