Rework progress bar and ui speed string so it gets the same value at a more accurate and snappier wall clock time

toolkit/progress_bar.py

@@ -4,6 +4,9 @@ import time
 
 class ToolkitProgressBar(tqdm):
     def __init__(self, *args, **kwargs):
+        # high EMA alpha so the rate/ETA responds within a few steps
+        # (tqdm default of 0.3 takes ~10 steps to wash out old samples)
+        kwargs.setdefault('smoothing', 0.7)
         super().__init__(*args, **kwargs)
         self.paused = False
         self.last_time = self._time()