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/GetUsageSummary/GetChannelUsageSummaryHandler.cs

@@ -1,4 +1,3 @@
-using HrynCo.DAL.Abstract;
 using HrynCo.NotificationService.DAL.Abstract.Repositories;
 using HrynCo.NotificationService.Services.Core;
 using HrynCo.NotificationService.Services.Logging;
@@ -13,9 +12,8 @@ internal sealed class GetChannelUsageSummaryHandler
 
     public GetChannelUsageSummaryHandler(
         IContextualSerilogLogger<GetChannelUsageSummaryQuery> logger,
-        IUnitOfWork unitOfWork,
         IEmailChannelRepository channelsRepository)
-        : base(logger, unitOfWork)
+        : base(logger)
     {
         _channelsRepository = channelsRepository;
     }