flow matching lcm scheduler (#11170)
* add flow matching lcm scheduler
* stochastic sampling
* upscaling for scale-wise generation
* Apply style fixes
* Apply suggestions from code review
Co-authored-by: hlky <hlky@hlky.ac>
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Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: YiYi Xu <yixu310@gmail.com>
Co-authored-by: hlky <hlky@hlky.ac>
