Add emeter support for strip sockets (#203)

* Add support for plugs with emeters.

* Tweaks for emeter

* black

* tweaks

* tweaks

* more tweaks

* dry

* flake8

* flake8

* legacy typing

* Update kasa/smartstrip.py

Co-authored-by: Teemu R. <tpr@iki.fi>

* reduce

* remove useless delegation

* tweaks

* tweaks

* dry

* tweak

* tweak

* tweak

* tweak

* update tests

* wrap

* preen

* prune

* prune

* prune

* guard

* adjust

* robust

* prune

* prune

* reduce dict lookups by 1

* Update kasa/smartstrip.py

Co-authored-by: Teemu R. <tpr@iki.fi>

* delete utils

* isort

Co-authored-by: Brendan Burns <brendan.d.burns@gmail.com>
Co-authored-by: Teemu R. <tpr@iki.fi>

kasa/tests/test_smartdevice.py

@@ -4,6 +4,7 @@ from unittest.mock import patch
 import pytest  # type: ignore # https://github.com/pytest-dev/pytest/issues/3342
 
 from kasa import SmartDeviceException
+from kasa.smartstrip import SmartStripPlug
 
 from .conftest import handle_turn_on, has_emeter, no_emeter, pytestmark, turn_on
 from .newfakes import PLUG_SCHEMA, TZ_SCHEMA, FakeTransportProtocol
@@ -26,7 +27,7 @@ async def test_initial_update_emeter(dev, mocker):
     dev._last_update = None
     spy = mocker.spy(dev.protocol, "query")
     await dev.update()
-    assert spy.call_count == 2
+    assert spy.call_count == 2 + len(dev.children)
 
 
 @no_emeter