Package-level declarations

The dynamics tier: a versor acts on shapes, a dynamics acts on entities. A dynamics is a stateless value applied to one entity with * — entity *= bounce(penetration) — performing a universal response every game would otherwise hand-roll, and demanding the entity's traits through its operator's generic bounds, so a missing trait is a compile error. Each dynamics is built by a lowercase-verb factory, and the moved entity comes back as its own class through its copy hook. Bounce is the first resident, resolving a Penetration as a perfectly elastic reflection.