fix: duration is an attribute of Interval, not Feature

pipeline/adjusters.py

@@ -68,7 +68,7 @@ class TargetTimeAdjuster(Adjuster):
 
         Pulled out for unit testing.
         """
-        return float(sum([x.duration for x in features]))
+        return float(sum([x.interval.duration for x in features]))
 
     def __init__(self, features: list=[],
                  target_time: int|float=_DEFAULT_TARGET_TIME,