Invert the start and end percentages in the code.

This doesn't affect how percentages behave in the frontend but breaks
things if you relied on them in the backend.

percent_to_sigma goes from 0 to 1.0 instead of 1.0 to 0 for less confusion.

Make percent 0 return an extremely large sigma and percent 1.0 return a
zero one to fix imprecision.

comfy/samplers.py

@@ -220,6 +220,8 @@ def sampling_function(model, x, timestep, uncond, cond, cond_scale, model_option
                         transformer_options["patches"] = patches
 
                 transformer_options["cond_or_uncond"] = cond_or_uncond[:]
+                transformer_options["sigmas"] = timestep
+
                 c['transformer_options'] = transformer_options
 
                 if 'model_function_wrapper' in model_options: