feat(infrastructure): add DbSetFactory registration in DependencyInjection

- Introduced AddDbSetFactory to support DbSet factory registration for entities.
- Updated RepositoryConfiguration.RegisterFromAssembly to register both repositories and DbSet factories.
- Changed RegisterFromAssembly and RegisterEntity to void methods instead of fluent interface.
- Extracted DbRepositoryFactory into its own Factory namespace for better separation of concerns.

DigitalData.Core.Infrastructure/Factory/DbSetFactory.cs

@@ -0,0 +1,13 @@
+using Microsoft.EntityFrameworkCore;
+
+namespace DigitalData.Core.Infrastructure.Factory;
+
+public class DbSetFactory<TDbContext,TEntity> where TDbContext : DbContext where TEntity : class
+{
+    public readonly Func<TDbContext, DbSet<TEntity>> Create;
+
+    public DbSetFactory(Func<TDbContext, DbSet<TEntity>> create)
+    {
+        Create = create;
+    }
+}