Make time remaining available for paused timers

[stefan-sherwood]

Is your feature request related to a problem? Please describe.

When I query a running timer, included is the fire_time field, from which I can subtract the current time to get the time remaining. However, when the timer status is paused the fire_time is null (as expected since the timer isn't running) and there is no other field I can use to determine how much time is left on the timer.

For example:

{
"entity_id": "sensor.home_base_timers",
    "state": "unavailable",
    "attributes": {
        "next_timer_status": "paused",
        "timers": [
            {
                "timer_id": "timer/9bed6d89-3091-43e0-80b4-5180dada71bb",
                "fire_time": null,
                "local_time": null,
                "local_time_iso": null,
                "duration": "0:05:00",
                "status": "paused",
                "label": "test timer"
            }
        ]
    }
}

Describe the solution you'd like

I recommend adding an additional field (e.g. remaining) that indicates how much time is remaining on the timer.

Describe alternatives you've considered

I tried having my program that queries the timer remember the fire_time and when the status changes to paused store the remaining time. This has two problems:

• by design there is potentially a huge latency between the time a timer changes state and the time that information is available in HA so this strategy can yield wildly inaccurate results
• if my program starts when there are already paused timers, there is no reference info available to get the time remaining

Additional context

If I go into the official Google Home Android app, I can see the time remaining on all existing timers, regardless of whether or not they are currently running. So I suspect this info is available.