dev: revert back to the old workstep.step's signature

Author: BillHuang2001

src/evox/workflows/std_workflow.py

@@ -252,7 +252,7 @@ def _step(self, state):
             for monitor in self.registered_hooks["post_step"]:
                 monitor.post_step(state)
 
-            return train_info, state
+            return state
 
         if self.jit_step:
             # the first argument is self, which should be static