introduce FrozenParam

For the case when the readback of a parameter does not reflect the
change immediately.

May also be used on Writable.target or Drivable.target with a short
BUSY period.

+ bug fix in an error message in frappy.datatypes.IntRange

Change-Id: I5e1c871629f9e3940ae80f35cb6307f404202b4a
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/31981
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

frappy/datatypes.py

@@ -315,7 +315,7 @@ class IntRange(DataType):
             except Exception:
                 raise WrongTypeError(f'can not convert {shortrepr(value)} to an int') from None
         if round(fvalue) != fvalue:
-            raise WrongTypeError('%r should be an int')
+            raise WrongTypeError(f'{value} should be an int')
         return value
 
     def validate(self, value, previous=None):