No user-facing tb even with invalid summary-format

If the user provides an invalid summary-format, we should:
 1. Continue with the execution
 2. Log a warning
 3. Fallback str rather than whatever fancy formatting

src/con_duct/__main__.py

@@ -578,7 +578,13 @@ def format_field(self, value: Any, format_spec: str) -> Any:
         if value is None:
             # TODO: could still use our formatter and make it red or smth like that
             return self.NONE
-        return super().format_field(value, format_spec)
+        try:
+            return super().format_field(value, format_spec)
+        except ValueError:
+            lgr.warning(
+                f"Value: {value} is invalid for format spec {format_spec}, falling back to `str`"
+            )
+            return str(value)
 
 
 @dataclass