[Feature] Implement OpenBLAS/LAPACK Backend

[csparker247]

Description

For users on HPC clusters where vendor-tuned BLAS/LAPACK (MKL, OpenBLAS) is preferred over Eigen, this backend provides a standardized interface to those C-based libraries.

Tasks

• Implement LapackBackend satisfying the MathBackend concept.
• Wrap standard BLAS/LAPACK calls for sparse matrix operations.
• Handle workspace memory allocations internally within the backend to keep the ABF++ algorithm "clean."