fix issues with lakeshore 370

- simplify parsing/formatting of LakeShore commands
  -> allow 'g' as enum format
- HasIO: check missing io later
- ls370res.ResChannel: get io for channels from switcher
- rwhandler.CommonWriteHandler: return value in write method
- frappy_psi.channelswitcher: fix the case when default channel does not exist

Change-Id: I28dd94cdf922cde307b870d4ffdfc64664c3423b
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/30949
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

frappy/rwhandler.py

@@ -217,6 +217,7 @@ class CommonWriteHandler(WriteHandler):
                     raise ProgrammingError('a method wrapped with CommonWriteHandler must not return any value')
                 # remove pname from writeDict. this was not removed in WriteParameters, as it was not missing
                 module.writeDict.pop(pname, None)
+            return getattr(module, pname)
         return method