Laplace Scheduler for DDPM (#11320)
* Add Laplace scheduler that samples more around mid-range noise levels (around log SNR=0), increasing performance (lower FID) with faster convergence speed, and robust to resolution and objective. Reference: https://arxiv.org/pdf/2407.03297.
* Fix copies.
* Apply style fixes
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Co-authored-by: YiYi Xu <yixu310@gmail.com>
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
