refactor: use low priority workqueue for underglow and battery reporting #5442

Job	Run time
get-grouped-hardware	12s
get-changed-files	3s
core-coverage	8s
nightly	0s
board-changes	0s
compile-matrix	2s
build (nice_nano_v2, [{"shield":"corne_left"},{"shield":"corne_right"},{"shield":"romac"},{"shiel...	6m 17s
build (nrfmicro_13, [{"shield":"corne_left"},{"shield":"corne_right"},{"shield":"romac"},{"shield...	4m 22s
build (proton_c, [{"shield":"corne_left"},{"shield":"corne_right"},{"shield":"romac"},{"shield":"...	2m 59s
build (bdn9_rev2, [{}])	1m 52s
build (nice60, [{}])	2m 27s
build (seeeduino_xiao_ble, [{"shield":"hummingbird"}])	2m 7s
build (nrf52840_m2, [{"shield":"m60"}])	2m 44s
build (planck_rev6, [{}])	2m 9s
build (nice_nano, [{"shield":"romac_plus","cmake-args":"-DCONFIG_ZMK_RGB_UNDERGLOW=y -DCONFIG_WS2...	2m 48s
	28m 10s

Provide feedback