initialVelocity should likely only be affected by _map when the shape of the type is going to change

[jverkoey]

trafficstars

E.g. .y() should extract the y velocity. yLocked(to:) should not affect the velocity. Over-applying _map's transform to initialVelocity can lead to nonsensical velocity values.

This may require operators to provide a separate velocity transform to _map.