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/CRUDControllerBaseWithErrorHandling.cs

@@ -1,4 +1,3 @@
-using DigitalData.Core.Abstractions;
 using DigitalData.Core.Application.Interfaces;
 using Microsoft.AspNetCore.Mvc;
 using DigitalData.Core.Application.DTO;
@@ -16,12 +15,13 @@ namespace DigitalData.Core.API
     /// <typeparam name="TId">The type of the entity's identifier.</typeparam>
     [ApiController]
     [Route("api/[controller]")]
+    [Obsolete("Use MediatR")]
     public class CRUDControllerBaseWithErrorHandling<TCRUDService, TCreateDto, TReadDto, TUpdateDto, TEntity, TId> : ControllerBase
         where TCRUDService : ICRUDService<TCreateDto, TReadDto, TEntity, TId>
         where TCreateDto : class
         where TReadDto : class
-        where TUpdateDto : class, IUnique<TId>
-        where TEntity : class, IUnique<TId>
+        where TUpdateDto : class
+        where TEntity : class
     {
         protected readonly ILogger _logger;
         protected readonly TCRUDService _service;