Detect offline hub children and fail fast on writes to them (#1830)

Hubs keep reporting for children they have lost contact with, so callers
see stale values as if they were live. Trying to write to such devices
fail after timeouts with a generic error.
This PR exposes the offline/online information as reported by the hub,
and refuses writes to unreachable child devices without waiting for
device errors.

In details:
- Add new API: `Device.is_available`; hub children report unavailable
when the hub marks them offline or no longer lists them.
- New feature `available` for child devices to make it visible to the
CLI.
- Refuse writes to unavailable children with the new
`DeviceUnavailableError` instead of waiting for the hub to time out.

kasa/smartcam/smartcamchild.py

@@ -85,6 +85,12 @@ class SmartCamChild(SmartChildDevice, SmartCamDevice):
         # devices
         self._info = self._map_child_info_from_parent(info)
 
+    @property
+    def is_available(self) -> bool:
+        """Return False if the hub reports the camera offline or no longer lists it."""
+        # Camera children report "online" instead of an "offline" status.
+        return super().is_available and self._info.get("online") is not False
+
     @property
     def device_type(self) -> DeviceType:
         """Return the device type."""

kasa/smartcam/smartcamdevice.py

@@ -215,7 +215,7 @@ class SmartCamDevice(SmartDevice):
     async def _query_setter_helper(
         self, method: str, module: str, section: str, params: dict | None = None
     ) -> dict:
-        res = await self.protocol.query({method: {module: {section: params}}})
+        res = await self._query_helper(method, {module: {section: params}})
 
         return res
 
@@ -293,10 +293,8 @@ class SmartCamDevice(SmartDevice):
 
     async def set_alias(self, alias: str) -> dict:
         """Set the device name (alias)."""
-        return await self.protocol.query(
-            {
-                "setDeviceAlias": {"system": {"sys": {"dev_alias": alias}}},
-            }
+        return await self._query_helper(
+            "setDeviceAlias", {"system": {"sys": {"dev_alias": alias}}}
         )
 
     @property