Use a grid meter component for testing EVChargerPool.power

This is because in the current component graph, there are no meters,
which is a problem because the mock resampler can't stream voltage
data for EV chargers, and the upcoming EVChargerManager requires
voltage info to determine the min and max power bounds for EV chargers
based on their rated current limits.

Signed-off-by: Sahas Subramanian <[email protected]>

Author: shsms

tests/timeseries/test_ev_charger_pool.py

@@ -19,7 +19,7 @@ async def test_ev_power(  # pylint: disable=too-many-locals
         mocker: MockerFixture,
     ) -> None:
         """Test the ev power formula."""
-        mockgrid = MockMicrogrid(grid_meter=False, mocker=mocker)
+        mockgrid = MockMicrogrid(grid_meter=True, mocker=mocker)
         mockgrid.add_ev_chargers(3)
 
         async with mockgrid: