Add conjugate gradient method for HyKKT #335
Description
Summary
HyKKT uses a specialized conjugate gradient that uses the Schur complement as an operator. We should have this functionality in ReSolve.
Rationale
We need this functionality to integrate the HyKKT solver.
Description
We should follow this implementation with setup and compute, taking care not to redo unnecessary steps. As usual with HyKKT, things that were originally implemented as CPU only should stay that way. Things that we implemented in CUDA only should have CPU and HIP versions as well. This is blocked by #311. It also requires things that should exist in ReSolve such as matrix vector multiplies, vector addition, dot products, and vector scaling. If they exist, adapt to existing implementations. If not, add them.
Additional information
No response