Implement action feature (#849)

Adds `FeatureType.Action` making it possible to expose features like
"reboot", "test alarm", "pair" etc.

The `attribute_getter` is no longer mandatory, but it will raise an
exception if not defined for other types than actions.
Trying to read returns a static string `<Action>`.
This overloads the `set_value` to call the given callable on any value.

This also fixes the `play` and `stop` coroutines of the alarm module to
await the call.

kasa/feature.py

@@ -17,7 +17,7 @@ class FeatureType(Enum):
     Sensor = auto()
     BinarySensor = auto()
     Switch = auto()
-    Button = auto()
+    Action = auto()
     Number = auto()
 
 
@@ -46,7 +46,7 @@ class Feature:
     #: User-friendly short description
     name: str
     #: Name of the property that allows accessing the value
-    attribute_getter: str | Callable
+    attribute_getter: str | Callable | None = None
     #: Name of the method that allows changing the value
     attribute_setter: str | None = None
     #: Container storing the data, this overrides 'device' for getters
@@ -95,6 +95,11 @@ class Feature:
     @property
     def value(self):
         """Return the current value."""
+        if self.type == FeatureType.Action:
+            return "<Action>"
+        if self.attribute_getter is None:
+            raise ValueError("Not an action and no attribute_getter set")
+
         container = self.container if self.container is not None else self.device
         if isinstance(self.attribute_getter, Callable):
             return self.attribute_getter(container)
@@ -112,6 +117,9 @@ class Feature:
                 )
 
         container = self.container if self.container is not None else self.device
+        if self.type == FeatureType.Action:
+            return await getattr(container, self.attribute_setter)()
+
         return await getattr(container, self.attribute_setter)(value)
 
     def __repr__(self):