allow for video imagen trainer to be instantiated from configs, with …

…a video boolean flag

allow unet3d to be created from config

allow for extrapolation to number of video frames outside of what was…

… trained on

allow for saving checkpoint without optimizer and scheduler

default self attention to false for unet3d, add example in readme

break parity with Jonathan Hos video diffusion paper, complete with c…

…ascading ddpm as well as elucidating ddpm, release 1.6.0

add ability to set bf16 mixed precision

fix a bug with order of normalizing and noising of the low resolution…

… conditioning image in non-elucidated ddpm, thanks to @animebing !