Deprecate repositories and update service interfaces

- Marked `IEnvelopeReceiverRepository` and several repository classes as obsolete, recommending the use of `IRepository`.
- Corrected `using` directive in `IReceiverService.cs`.
- Removed `UpdateAsync` method from `IReceiverService`.
- Enhanced `ISmsSender` interface with new properties and methods.
- Updated `ReceiverCreateDto`, `ReceiverReadDto`, and `UserReceiverDto` to enforce non-nullable properties.
- Refactored `TestReceiverController` to suggest using `MediatR`.

EnvelopeGenerator.Application/Contracts/Repositories/IEnvelopeReceiverRepository.cs

@@ -6,6 +6,7 @@ namespace EnvelopeGenerator.Application.Contracts.Repositories;
 /// <summary>
 /// 
 /// </summary>
+[Obsolete("Use IRepository")]
 public interface IEnvelopeReceiverRepository : ICRUDRepository<EnvelopeReceiver, (int Envelope, int Receiver)>
 {
     /// <summary>