Function solve_space_prime_power 

pub fn solve_space_prime_power(
    equations: &[ModpEquation],
    num_vars: usize,
    p: u64,
    k: u32,
) -> Option<PrimePowerSpace>

Solve a ℤ/pᵏ system for its full solution space via Smith normal form U·A·V = D — the scalable analogue of crate::modp::solve_space over a prime-power ring (where p is a zero-divisor, so field Gaussian fails). Returns the particular solution plus the kernel generators (so a variable the kernel never moves is forced), or Inconsistent. None only when the integer Smith reduction overflows [GROWTH_CAP]. k = 1 delegates to the prime-field solver.