Update api.py

Author: avdudchenko

src/idaes_flowsheet_processor/api.py

@@ -39,7 +39,7 @@
     import importlib_metadata as metadata
 
 # third-party
-from pyomo.contrib.viewer.report import degrees_of_freedom
+from idaes.core.util.model_statistics import degrees_of_freedom
 from pydantic import BaseModel, Field, field_validator, ValidationInfo, ConfigDict
 import pyomo.environ as pyo