* feat: add U-Net specials of SDXS
* docs: update distilled_sd.md for SDXS-512
* feat: for SDXS use AutoencoderTiny as the primary VAE
* docs: update distilled_sd.md for SDXS-512
* fix: SDXS code cleaning after review by stduhpf
* format code
* fix sdxs with --taesd-preview-only
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Co-authored-by: leejet <leejet714@gmail.com>