Refactor namespaces and update DTO structures

Updated namespaces for DTOs and services to improve project organization. Marked several interfaces as obsolete in favor of MediatR for better request handling. Simplified `BaseUpdateDto` and other DTOs by removing `IUnique<int>` implementation. Changed return types of `CreateAsync` methods to return corresponding read DTOs. Removed reference to `DigitalData.Core.DTO` in the project file, reflecting a shift in architecture for maintainability.

DigitalData.UserManager.Application/Contracts/IUserRepService.cs

@@ -1,9 +1,10 @@
 using DigitalData.UserManager.Application.DTOs.UserRep;
 using DigitalData.UserManager.Domain.Entities;
-using DigitalData.Core.DTO;
+using DigitalData.Core.Abstraction.Application.DTO;
 
 namespace DigitalData.UserManager.Application.Contracts
 {
+    [Obsolete("Use MediatR")]
     public interface IUserRepService : IBaseService<UserRepCreateDto, UserRepReadDto, UserRep>
     {
         Task<DataResult<IEnumerable<UserRepReadDto>>> ReadAllAsync(bool withUser = false, bool withRepGroup = false, bool withGroup = false, bool withRepUser = false, int? userId = null, int? groupId = null);