Split the Rapier world's pending-command staging into its own class, move
collider derivation out of the body, separate drive configuration, effort,
and continuous-angle tracking from joint creation, and break the USD entry
points into named steps. Share axisVector, wrapAngle, and ancestorBody
instead of copies.

Worlds expose disposed and share one set of assertions, joints gain
connects(body), and the index lists its exports explicitly with adapter
helpers grouped in one module. Package manifests use main and types
instead of an exports map.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>