new structure for ptychoengine

ptycho/base.py

@@ -7,8 +7,13 @@ class PtychoEngine(ABC):
 
     def __init__(self, config):
         self.config = config
-
+        self._verbosity = self.config['io'].get('verbosity', 0)
+        self._output = None
 
     @abstractmethod
     def run(self, run_id="") -> None:
         pass
+
+    @abstractmethod
+    def metric(self, names: str | list[str]) -> float | list[float]:
+        pass