Add sparse matrix-matrix product and addition capabilities to HyKKT

[shakedregev]

Summary

Sparse matrix-matrix multiplication and addition as here with tests. It's very hard to create a generic test for this, so a specific test is fine. Unfortunately there is no corresponding test in the HyKKT repo.

Rationale

SPGEMM (sparse general matrix multiplication) and addition (which is implicit) are essential for HyKKT to work. This could also be used if other methods need it.

Description

1. Any originally cpu functions need only have cpu implementations
2. Any originally gpu functions should have cpu/cuda/hip support.
3. Write tests as within the rest of ReSolve.
4. An idea I have for a test is to do the matrix product in python/julia and have a known output to check against.

Additional information

No response