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.Infrastructure/Repositories/ReceiverRepository.cs

@@ -5,6 +5,7 @@ using Microsoft.EntityFrameworkCore;
 
 namespace EnvelopeGenerator.Infrastructure.Repositories;
 
+[Obsolete("Use IRepository")]
 public class ReceiverRepository : CRUDRepository<Receiver, int, EGDbContext>, IReceiverRepository
 {
     public ReceiverRepository(EGDbContext dbContext) : base(dbContext, dbContext.Receivers)