fix: filter garbage data from Daikin API responses

[gcamp]

The Daikin API occasionally returns sentinel values (255, 65535) when the thermostat restarts or loses connectivity. These garbage values result in unrealistic sensor readings like 127.5% demand or 655.35kW power usage.

This change adds validation to detect these sentinel values and skip updates with corrupted data, preserving the last known good state instead. A warning is logged when garbage data is detected for debugging purposes.

Fixes #79

[gcamp]

@zlangbert any chance for a review and merge? This project seems unmaintained at this point

[zlangbert]

Hi @gcamp, thanks for the PR and ping, I've been meaning to come back to this at some point.

When I was initially looking at this (#22), I remember thinking I wanted to filter out specific sensor updates with sentinel values rather than not update anything. The reasoning being I couldn't be sure that we wouldn't get sentinel values for one thing and not another, potentially blocking updates to new values we do want.

Now that you have looked into this more, any additional insight on that? How confident are you in this approach?

[gcamp]

Hard to be confident at 100% when you're working on an private API but I can say that :

• When this issue happens, all the values are set to the sentinel value (see response in Daikin API sometimes sends garbage data, should filter #79)
• I don't see how a functioning unit could return sentinel values for any of the fields listed (it does still return sentinel for some values, but not any of the required fields).
  • Does Daikin still has some AC that aren't heatpump? In that case we can probably check heat or cold instead of heat and cold.
  • I was initially wrong about ctIFCFanRequestedDemandPercent being required, which I don't understand because I don't see my fan_demand_requested at 127%. I didn't investigate more at this point.

I also added tests, but feel free to remove them if you don't think they add value (since there was no test before).

Currently testing my branch on my home assistant, I can report back in a week or two to make sure everything is good.

[zlangbert]

Does Daikin still has some AC that aren't heatpump? In that case we can probably check heat or cold instead of heat and cold.

This is essentially the issue I am most concerned about. I have seen a lot of different combinations of reported / non-reported values for people with differing equipment, some of which I can't make any sense of. The more I think about this the more I feel we should take a more granular approach.

My philosophy at this point is the less we assume about the relationships between fields the better