kded: Consult Bluez to get battery percentage
While PulseAudio exposed the battery percentage as "bluetooth.battery" property, with Pipewire there's just general Bluez device information.
Since we currently don't show battery percentage anywhere else, we can just ask Bluez on the spot, rather than pull in Bluez-Qt and do proper change tracking.
Not super happy but also quite straightforward and encapsulated.
Fixes my headphone battery state not being shown anymore when I switch to it on neon 24.04