Fix Powerpal Readings API sensors

[azz]

I was getting astronomical figures reported to Powerpal Cloud!

Turned out the "Watt Hours" sensor was off by a factor of my meter pulse rate (3.200) squared. After some quick algebra I realised the calculation inside this module was incorrect.

For reference, my rest_command looks like this:

rest_command:
  send_readings_to_powerpal_cloud:
    url: "https://readings.powerpal.net/api/v1/meter_reading/{{POWERPAL_DEVICE_ID}}"
    method: POST
    headers:
      authorization: "{{POWERPAL_API_KEY}}"
      accept: ""
    payload: >-
       {% set readings = [{
            "is_peak": false, 
            "pulses": states('sensor.powerpal_pulses') | int, 
            "timestamp": now() | as_timestamp | int // 60 * 60,
            "watt_hours": states('sensor.powerpal_watt_hours') | float
        }] %}
        {{ readings | to_json }}
    content_type: 'application/json'
    verify_ssl: true

and I have an automation that kicks off for each change to the "Daily Pulses" sensor:

alias: PowerPal - Send Readings to Cloud
description: ""
triggers:
  - trigger: state
    entity_id:
      - sensor.powerpal_daily_pulses
    from: null
    enabled: true
conditions: []
actions:
  - action: rest_command.send_readings_to_powerpal_cloud
    metadata: {}
    data: {}
    response_variable: api_response
mode: single

Interestingly, I noticed that the "Powerpal Timestamp" sensor only seems to update every 2-3 minutes, instead of every minute. It appears that while a set of values is produced every minute, sometimes the timestamp in the BLE packet doesn't change, so in my automation I have just used now() | as_timestamp | int // 60 * 60, which seems to do the trick.