payment.data library Null safety

Data layer for Booking and Payment feature.

Classes

BookingModel
Booking data model
BookingRepository
Booking repository implementation of IBookingRepository
BookingService
Booking data source implementation of IBookingService using httpClient
IBookingService
Booking data source abstract service
IPaymentService
Payment data source abstract service
PaymentRepository
Payment repository interface of IPaymentRepository
PaymentService
Payment data source implementation of IBookingService using httpClient