Function std::dpm_solver_pp_1_step

&FloatTensor dpm_solver_pp_1_step(
    const &FloatTensor x_cur,
    const &FloatTensor x0Pred,
    float alpha_cur,
    float sigma_cur,
    float alpha_next,
    float sigma_next,
)

Same exponential-integrator idea as DPM-Solver, reformulated around a predicted x0 (the denoised sample) instead of a predicted eps (the noise). Order-1 is provably identical to ddim_sampler_step — see diffusion.sc's header comment for the derivation.