SOLVAX: differentiable structured linear solvers, preconditioners and matrix-free methods in JAX

Differentiable structured direct solves, preconditioned and recycled Krylov methods, physics-agnostic preconditioners, mixed-precision iterative refinement, and structure-preserving discrete adjoints, all jit/vmap/grad-transparent on CPU and GPU. Releases archive the library together with its benchmark drivers and committed measurement records for independent reproduction.