requency at which the callback function is called. If not specified, the callback is called at
every step.
extra_step_kwargs —
Extra_step_kwargs.
cross_attention_kwargs —
A kwargs dictionary that if specified is passed along to the AttentionProcessor as defined in
self.processor.
num_warmup_steps —
number of warmup steps.   Returns 
latents
  
latents of backward process output at time timesteps[-1]
  Perform backward process given list of time