Update load class methods to use new statistics path

[firewiremb]

Along with the API v2 the structure of the 'load class' information has changed. See also #650

[CFenner]

Do you have related testdata that we can update as well?

[firewiremb]

Test data:

{
  "apiVersion": 1,
  "commands": {},
  "deviceId": "0",
  "feature": "heating.compressors.0.statistics.load",
  "gatewayId": "################",
  "isEnabled": true,
  "isReady": true,
  "properties": {
    "hoursLoadClassFive": {
      "type": "number",
      "unit": "hour",
      "value": 432
    },
    "hoursLoadClassFour": {
      "type": "number",
      "unit": "hour",
      "value": 1108
    },
    "hoursLoadClassOne": {
      "type": "number",
      "unit": "hour",
      "value": 83
    },
    "hoursLoadClassThree": {
      "type": "number",
      "unit": "hour",
      "value": 2852
    },
    "hoursLoadClassTwo": {
      "type": "number",
      "unit": "hour",
      "value": 858
    }
  },
  "timestamp": "2026-01-27T03:42:50.961Z",
  "uri": "https://api.viessmann-climatesolutions.com/iot/v2/features/installations/30361/gateways/################/devices/0/features/heating.compressors.0.statistics.load"
},

Vitocal_300G.json