Add ruff fixes

Author: t-sommer

src/sdf/__init__.py

@@ -156,7 +156,7 @@ def _validate_group(group, is_root=False):
 
 def _validate_dataset(ds):
 
-    if not type(ds.data) is np.ndarray:
+    if type(ds.data) is not np.ndarray:
         return ['Dataset.data must be a numpy.ndarray']
 
     elif ds.data.size < 1:

src/sdf/examples/plot_dymola_result.py

@@ -1,5 +1,4 @@
 import sdf
-from sdf.plot.plot_time_series import plot_time_series
 import matplotlib.pyplot as plt