refactor: replace internal UnitOfWork with NotificationUnitOfWork and NotificationBaseRepository

- Consolidate unit of work implementation with NotificationUnitOfWork.
- Refactor repositories to use NotificationBaseRepository for consistency.
- Simplify request handlers by removing IUnitOfWork dependency.
- Update related tests and service registration.

HrynCo.NotificationService.Services/EmailChannels/Get/GetEmailChannelHandler.cs

@@ -1,4 +1,3 @@
-using HrynCo.DAL.Abstract;
 using HrynCo.NotificationService.DAL.Abstract.Providers;
 using HrynCo.NotificationService.DAL.Abstract.Repositories;
 using HrynCo.NotificationService.Services.Core;
@@ -14,9 +13,8 @@ internal sealed class GetEmailChannelHandler
 
     public GetEmailChannelHandler(
         IContextualSerilogLogger<GetEmailChannelQuery> logger,
-        IUnitOfWork unitOfWork,
         IEmailChannelRepository channels)
-        : base(logger, unitOfWork)
+        : base(logger)
     {
         _channels = channels;
     }