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8e74efad - Add Singlestep DPM-Solver (singlestep high-order schedulers) (#1442)

Add Singlestep DPM-Solver (singlestep high-order schedulers) (#1442) * add singlestep dpmsolver * fix a style typo * fix a style typo * add docs * finish Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>