fix(dfn): keep block attribute for now (#182)

Flopy expects this for mfstructure.py introspection. Keep it for now and drop it once flopy no longer needs it.

modflow_devtools/dfn.py

@@ -435,7 +435,7 @@ def _fields() -> Vars:
 
         # remove unneeded variable attributes
         def remove_attrs(path, key, value):
-            if key in ["block", "in_record", "tagged", "preserve_case"]:
+            if key in ["in_record", "tagged", "preserve_case"]:
                 return False
             return True