Deprecate controllers/services; simplify generics

Added `[Obsolete("Use MediatR")]` attributes to various controller and service classes to indicate deprecation in favor of MediatR. Simplified generic type constraints in `CRUDControllerBase` and related files by removing `IUnique<TId>`. Improved structure and documentation in `CSPMiddleware.cs`. Introduced new extension methods in `EntityExtensions.cs` for safer retrieval of 'Id' properties. Removed `IUnique.cs` interface and updated project dependencies in `DigitalData.Core.Application.csproj` for caching. Overall, these changes enhance code maintainability and clarity.

DigitalData.Core.API/ReadControllerBaseWithErrorHandling.cs

@@ -13,6 +13,7 @@ namespace DigitalData.Core.API
     /// <typeparam name="TId">The type of the entity's identifier.</typeparam>
     [ApiController]
     [Route("api/[controller]")]
+    [Obsolete("Use MediatR")]
     public class ReadControllerBaseWithErrorHandling<TReadService, TReadDto, TEntity, TId> : ControllerBase
         where TReadService : IReadService<TReadDto, TEntity, TId>
         where TReadDto : class