[utils] Identity*Identity = Identity ;)
[utils] rewrite norm + inner

[skip ci]
[utils] include preconditioning in Arnoldi

[skip ci]
[utils] Arnoldi/Lanczos fixes
[linsys] new Minres class
[linsys] allow Minres with other orthogonalizations

[skip ci]
[linsys,tests] let Minres pass tests