Avoid linear search for emeter realtime and emeter_today (#622)

* Avoid linear search for emeter realtime and emeter_today

Most of the time the data we want is at the end of the
list so we now search backwards to avoid having to
scale all the data and throw most of it away

* more tweaks

* coverage

* coverage

* preen

* coverage

* branch cover

kasa/tests/test_emeter.py

@@ -1,6 +1,10 @@
+import datetime
+from unittest.mock import Mock
+
 import pytest
 
 from kasa import EmeterStatus, SmartDeviceException
+from kasa.modules.emeter import Emeter
 
 from .conftest import has_emeter, has_emeter_iot, no_emeter
 from .newfakes import CURRENT_CONSUMPTION_SCHEMA
@@ -116,3 +120,29 @@ async def test_emeterstatus_missing_current():
 
     missing_current = EmeterStatus({"err_code": 0, "power_mw": 0, "total_wh": 13})
     assert missing_current["current"] is None
+
+
+async def test_emeter_daily():
+    """Test fetching the emeter for today.
+
+    This test uses inline data since the fixtures
+    will not have data for the current day.
+    """
+    emeter_data = {
+        "get_daystat": {
+            "day_list": [{"day": 1, "energy_wh": 8, "month": 1, "year": 2023}],
+            "err_code": 0,
+        }
+    }
+
+    class MockEmeter(Emeter):
+        @property
+        def data(self):
+            return emeter_data
+
+    emeter = MockEmeter(Mock(), "emeter")
+    now = datetime.datetime.now()
+    emeter_data["get_daystat"]["day_list"].append(
+        {"day": now.day, "energy_wh": 500, "month": now.month, "year": now.year}
+    )
+    assert emeter.emeter_today == 0.500