fix interplay mercury.TemperatureLoop and HasConvergence

frappy_psi.convergence.HasConvergence:
- no need to inherit HasStates (should be independent)
- trigger current state then tolerance or settling_time is changed

frappy_psi.mercury:
- improve readback checks
- fix interplay with HasControlledBy
- fix interplay with HasConvergence

Change-Id: I6efedbe6bbfba5a66ddd22ac441ebf38af11eda6
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/31047
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

frappy/lib/__init__.py

@@ -396,3 +396,13 @@ class UniqueObject:
 
     def __repr__(self):
         return self.name
+
+
+def merge_status(*args):
+    """merge status
+
+    the status with biggest code wins
+    texts matching maximal code are joined with ', '
+    """
+    maxcode = max(a[0] for a in args)
+    return maxcode, ', '.join([a[1] for a in args if a[0] == maxcode and a[1]])