Fix battery sensor to align with new structure

[themoosman]

The battery sensor in HA has been broken for quite a while. Upon investigation, the Vehicles API response has changed. battery is no longer under mil.

Here is a current JSON payload from the API.

    {
      "model": { "make": "HONDA", "name": "Pilot", "year": 2019 },
      "nickName": "Pilot",
      "standardEngine": "3.5L V6",
      "vin": "8675309",
      "imei": "1234567890",
      "stats": {
        "localTimeZone": "-0600",
        "lastUpdated": "2024-12-08T22:34:01.000Z",
        "odometer": 3332,
        "location": {
          "lat": 123.000,
          "lon": -123.000,
          "heading": 36,
          "address": null
        },
        "fuelLevel": 86.4857712277679,
        "isRunning": false,
        "speed": 0,
        "mil": {
          "milOn": false,
          "lastUpdated": "2023-10-15T03:01:00.000Z",
          "qualifiedDtcList": []
        },
        "battery": {
          "status": "normal",
          "lastUpdated": "2024-12-01T22:34:44.000Z"
        }
      }
    }

This PR maps the sensor to the new JSON structure and updates the unit tests.