Enhance IRepository and update DbRepositoryTests

- Added ReadAsync method to IRepository for user retrieval.
- Introduced _userRepo field in DbRepositoryTests for better clarity.
- Modified Setup method to initialize _userRepo from the service provider.
- Updated CreateAsync_ShouldNotThrow to use _userRepo.
- Added ReadAsync_ShouldReturnCreated test for user retrieval validation.

DigitalData.Core.Abstractions/Infrastructure/IRepository.cs

@@ -17,4 +17,5 @@ public interface IRepository<TEntity>
     public Task UpdateAsync<TDto>(TDto dto, Expression<Func<TEntity, bool>> expression, CancellationToken ct = default);
 
     public Task DeleteAsync<TDto>(Expression<Func<TEntity, bool>> expression, CancellationToken ct = default);
+    Task ReadAsync(Core.Tests.Mock.User user);
 }