HHL quantum linear-system solver for Hermitian A and power-of-two dimension N. This implementation accepts user-provided A and b, auto-computes the evolution time t, uses QPE with U = exp(i2πAt), and reconstructs an approximate classical solution from post-selection in a statevector simulation; exponential speedup claims require sparse/block-encoded access, efficient state preparation, bounded condition number, efficient Hamiltonian simulation, and partial readout rather than full classical-vector recovery.
