schedulers/dpmsolver_multistep: add missing sde-dpmsolver branch in third-order update

[Dev-X25874]

This happens silently after the two lower-order warm-up steps complete (i.e. on step 3+),
making it a hard runtime crash for any user who configures sde-dpmsolver with
solver_order=3.

The fix adds the missing elif self.config.algorithm_type == "sde-dpmsolver" branch,
derived from the same factor-of-2 doubling pattern that governs the sde-dpmsolver
formulation relative to dpmsolver at every other order (per Appendix A of the
DPMSolver paper), and using the identical
noise term sigma_t * sqrt(exp(2h) - 1) * noise already present in the 1st- and
2nd-order sde-dpmsolver branches.

Fixes # (issue)

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