The Pipeline class has a friend class PipelineD which breaks some Pipeline class encapsulation. We should check if PipelineD can operate only on Pipeline's public interface which is already quite permissive, and, if it possible, rewrite PipelineD methods and remove the undesired friendship.

This ticket is related to the ongoing refactoring of the Pipeline class within SPM-4106, but it is not a part of the project's scope and can be processed independently.