Immediate-mode simulation

Sometimes it is useful to simulate motion for a single object without updating the entire world. For example, in a networked multiplayer game, it might be necessary for a server to compute the motion of an object thrown by a remote player for several timesteps while time does not otherwise advance, to bring the server's model of the object into sync with the player's client-side prediction.

Rapier already supports computing contact manifolds independently of the progression of time via the `QueryPipeline`. A complete solution would expand on this with helpers to compute contact resolution forces and to integrate motion, with or without CCD. A higher-level `step`-like interface that bundles these up might be useful as well, though it's unclear if that might be significantly less flexible.

[PhysX's immediate mode API](https://docs.nvidia.com/gameworks/content/gameworkslibrary/physx/guide/Manual/RigidBodyDynamics.html#immediate-mode) is prior art.