[hdpowerview] Firmware versions are fetched at every poll cycle

[jlaur]

Expected Behavior

Firmware versions should be fetched when binding is initialized, and optionally with low frequency after that.

Current Behavior

Version information is fetched at every poll cycle, i.e. once per minute with default settings.

Possible Solution

Root cause is that method updateFirmwareProperties does not cache the firmware information instance variable firmwareVersions, but only in local variable of same name. The reason why the instance variable was introduced was having the ability to check cached firmware version in logic which needed to know whether on V1 or V2 hub because of #11856. However, the final fix didn't need this information after all, so it should be dropped and replaced by a timestamp instead, so it could be invalidated after some time.

Steps to Reproduce

Enable debug logging and observe that GET /api/fwversion requests are made every minute:

2022-07-21 11:42:52.649 [DEBUG] [ternal.handler.HDPowerViewHubHandler] - Main processor firmware version received: PV Hub2.0, 2.0.1056
2022-07-21 11:42:52.660 [DEBUG] [ternal.handler.HDPowerViewHubHandler] - Radio firmware version received: 2.0.2610

Context

This is a regression of #11979.