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.DAL.EF/NotificationUnitOfWork.cs

@@ -0,0 +1,10 @@
+namespace HrynCo.NotificationService.DAL.EF;
+
+using HrynCo.DAL.EF.Core;
+
+public class NotificationUnitOfWork : EfUnitOfWork<NotificationDbContext>
+{
+    public NotificationUnitOfWork(NotificationDbContext context) : base(context)
+    {
+    }
+}