Improve feature setter robustness (#870)

This adds a test to check that all feature.set_value() calls will cause
a query, i.e., that there are no self.call()s that are not awaited, and
fixes existing code in this context.

This also fixes an issue where it was not possible to print out the
feature if the value threw an exception.

kasa/feature.py

@@ -172,9 +172,14 @@ class Feature:
         return await getattr(container, self.attribute_setter)(value)
 
     def __repr__(self):
-        value = self.value
+        try:
+            value = self.value
+        except Exception as ex:
+            return f"Unable to read value ({self.id}): {ex}"
+
         if self.precision_hint is not None and value is not None:
             value = round(self.value, self.precision_hint)
+
         s = f"{self.name} ({self.id}): {value}"
         if self.unit is not None:
             s += f" {self.unit}"