Fix flaky test in hydrawise by falling back to main coordinator data

When new zones/controllers are discovered by the main coordinator,
entities may be created for the water_use coordinator before it has
refreshed. This caused KeyError when accessing zones/controllers
that exist in the main coordinator but not yet in the water_use
coordinator's data.

The fix adds a _get_data() method that checks if the entity's
controller/zone exists in the current coordinator's data, and falls
back to the main coordinator's data if not. This also handles the
case when controllers/zones are removed - the entity gracefully
skips updating instead of raising KeyError.

homeassistant/components/hydrawise/entity.py

@@ -10,7 +10,11 @@ from homeassistant.helpers.entity import EntityDescription
 from homeassistant.helpers.update_coordinator import CoordinatorEntity
 
 from .const import DOMAIN, MANUFACTURER, MODEL_ZONE
-from .coordinator import HydrawiseDataUpdateCoordinator
+from .coordinator import (
+    HydrawiseData,
+    HydrawiseDataUpdateCoordinator,
+    HydrawiseWaterUseDataUpdateCoordinator,
+)
 
 
 class HydrawiseEntity(CoordinatorEntity[HydrawiseDataUpdateCoordinator]):
@@ -50,11 +54,29 @@ class HydrawiseEntity(CoordinatorEntity[HydrawiseDataUpdateCoordinator]):
             self._attr_device_info["via_device"] = (DOMAIN, str(controller.id))
         self._update_attrs()
 
+    def _get_data(self) -> HydrawiseData:
+        """Return coordinator data with fallback to main coordinator.
+
+        When new zones/controllers are discovered, entities may be created
+        before the water_use coordinator has refreshed. In this case, fall
+        back to the main coordinator's data which has the latest information.
+        """
+        data: HydrawiseData = self.coordinator.data
+        if isinstance(self.coordinator, HydrawiseWaterUseDataUpdateCoordinator):
+            main_data = self.coordinator._main_coordinator.data  # noqa: SLF001
+            # Check if this entity's controller/zone exists in current data
+            if (
+                self.controller.id not in data.controllers
+                or (self.zone_id is not None and self.zone_id not in data.zones)
+            ):
+                data = main_data
+        return data
+
     @property
     def zone(self) -> Zone:
         """Return the entity zone."""
         assert self.zone_id is not None  # needed for mypy
-        return self.coordinator.data.zones[self.zone_id]
+        return self._get_data().zones[self.zone_id]
 
     @property
     def sensor(self) -> Sensor:
@@ -69,8 +91,10 @@ class HydrawiseEntity(CoordinatorEntity[HydrawiseDataUpdateCoordinator]):
     @callback
     def _handle_coordinator_update(self) -> None:
         """Get the latest data and updates the state."""
-        self.controller = self.coordinator.data.controllers[self.controller.id]
-        self._update_attrs()
+        data = self._get_data()
+        if self.controller.id in data.controllers:
+            self.controller = data.controllers[self.controller.id]
+            self._update_attrs()
         super()._handle_coordinator_update()
 
     @property