Newton hard-codes BlockVector for solver
I had a case where I wrote a linear solver that works with DynamicVector and DynamicMatrix. I couldn't use this solver in the Newton because at some point the Newton copies everything to a BlockVector to support UMFPack. I think this should be more fine grained and only convert if necessary. And make sure it converts to the type that the solver expects. With !2113 it should be possible to know the type the solver expects.