refactor: assertion

Author: msto

fgpyo/util/metric.py

@@ -460,9 +460,7 @@ def __init__(
         filepath: Path = filename if isinstance(filename, Path) else Path(filename)
         file_format = MetricFileFormat(delimiter=delimiter)
 
-        assert is_metric(
-            metric_class
-        ), "Metric class must be a dataclass- or attr-decorated subclass of `Metric`."
+        assert_is_metric(metric_class)
         io.assert_path_is_writeable(filepath)
         if append:
             io.assert_path_is_readable(filepath)