waterleaksensor: use parent's Time for alert timestamp (#1614)

We do not, by design, add Time module for hub's children.
This has a side-effect that we need to fallback to the parent's time
module to allow presenting the correct timestamp for the last alert.

tests/smart/modules/test_waterleak.py

@@ -5,6 +5,7 @@ import pytest
 
 from kasa.smart.modules import WaterleakSensor
 
+from ...conftest import get_device_for_fixture_protocol
 from ...device_fixtures import parametrize
 
 waterleak = parametrize(
@@ -12,6 +13,12 @@ waterleak = parametrize(
 )
 
 
+@pytest.fixture
+async def parent(request):
+    """Get a dummy parent for tz tests."""
+    return await get_device_for_fixture_protocol("H100(EU)_1.0_1.5.5.json", "SMART")
+
+
 @waterleak
 @pytest.mark.parametrize(
     ("feature", "prop_name", "type"),
@@ -21,8 +28,9 @@ waterleak = parametrize(
         ("water_leak", "status", Enum),
     ],
 )
-async def test_waterleak_properties(dev, feature, prop_name, type):
+async def test_waterleak_properties(dev, parent, feature, prop_name, type):
     """Test that features are registered and work as expected."""
+    dev._parent = parent
     waterleak: WaterleakSensor = dev.modules["WaterleakSensor"]
 
     prop = getattr(waterleak, prop_name)
@@ -34,8 +42,9 @@ async def test_waterleak_properties(dev, feature, prop_name, type):
 
 
 @waterleak
-async def test_waterleak_features(dev):
+async def test_waterleak_features(dev, parent):
     """Test waterleak features."""
+    dev._parent = parent
     waterleak: WaterleakSensor = dev.modules["WaterleakSensor"]
 
     assert "water_leak" in dev.features
@@ -43,3 +52,6 @@ async def test_waterleak_features(dev):
 
     assert "water_alert" in dev.features
     assert dev.features["water_alert"].value == waterleak.alert
+
+    assert "water_alert_timestamp" in dev.features
+    assert dev.features["water_alert_timestamp"].value == waterleak.alert_timestamp