psl::ecs::details::dependency_pack class

describes a set of dependencies for a given system

systems can have various dependencies, for example a movement system could have dependencies on both a psl::ecs::components::transform component and a psl::ecs::components::renderable component. This dependency will output a set of psl::ecs::entity_t's that have all required psl::ecs::components present. Certain systems could have sets of dependencies, for example the render system requires knowing about both all psl::ecs::components::renderable that have a psl::ecs::components::transform, but also needs to know all psl::ecs::components::camera's. So that system would require several dependency_pack's.