ENH: LambVector FO is expensive to compute

Problem statement: LambVector expression is (\nabla \times \mathbf{u}) \times \mathbf{u}, which revealed to be expensive to compute.

Problem solution: Equivalent expressions, and potential simplifications, e.g. for incompressible flow computations, may reduce the computational cost of LambVector.

Most of the time the divergence of LambVector is the actual field of interest rather than the LambVector itself.

Nevertheless, the divergence of lambVector is computed by an external div FO. Instead, \nabla \cdot ((\nabla \times \mathbf{u})\times \mathbf{u}) may be further reduced to a simpler form.