Euler has "isEuler", Vector3 has "isVector3"... etc. etc.  Quaternion does not.

improve performance of Vector3.(un)project, Matrix4.multiplyMatrices is more expensive than Vector3.applyMatrix4

Chromatic lerp using hsl unlike linear one using rgb

Previous implementation relied on average quaternions (t=0.5) for small angles.
Now uses the same approach as Quaternion.slerpFlat (threshold and lerp)