Updated code to support conditional compilation for .NET Framework and .NET.
Introduced nullable reference types in `DbRepository.cs` and ensured proper initialization of service registration queues in `DependencyInjection.cs`.
Modified `DbRepositoryFactory.cs` and `DbSetFactory.cs` to maintain consistent structure across frameworks.
These changes enhance compatibility and improve type safety.
- 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.
