Add num_timesteps for callback kwargs

pipeline.py

@@ -897,6 +897,7 @@ class FluxDifferentialImg2ImgPipeline(DiffusionPipeline, FluxLoraLoaderMixin):
         # end diff diff preparation
 
         num_warmup_steps = max(len(timesteps) - num_inference_steps * self.scheduler.order, 0)
+        self._num_timesteps = len(timesteps)
 
         # 6. Denoising loop
         latents_dtype = latents.dtype