How do you speed up the linear sparse solver in Zygote?

[stevengj]

@ChrisRackauckas

It adds rules for Zygote and Enzyme and wraps pretty much every linear solver that people use in practice. That should handle this just fine?

To compute \nabla_x \Vert A(x)^{-1} b \Vert with current AD tools where A(x) is sparse, you still have the problem of trying to differentiate through the sparse-matrix constructor, no?