Piece colvol rotation

Consider a starfish-style 5-legged unit like this:

Say I want each leg to have a per-piece colvol. Right now colvols are oriented alongside cardinal directions, so have to look like this:

The request is to add some way to make it possible for them to look like this:

`Spring.SetUnitPieceCollisionVolumeData` lets us change scale and offset of these colvols, but not the rotation. Perhaps split the above into `spSetUnitPieceCollisionVolumeScale` and `spSetUnitPieceCollisionVolumeOffsets` and add `spSetUnitPieceCollisionVolumeRotation` to match?

Start by tracing the implementation and bindings for Spring.SetUnitPieceCollisionVolumeData, focusing on how per-piece scale and offset are stored and applied. Compare the existing collision-volume API with the requested rotation support; done means starfish-style pieces can orient each collision volume independently without losing scale or offset behavior.

Written by the indexing model from the issue text.