Use constant-time comparison for MAC verification #182

Job	Run time
build (RAK_4631_companion_radio_ble)	2m 30s
build (Heltec_v3_room_server)	2m 55s
build (Heltec_v3_repeater)	3m 5s
build (RAK_4631_repeater)	1m 36s
build (wio-e5-mini_repeater)	1m 37s
build (RAK_4631_room_server)	2m 17s
build (PicoW_repeater)	2m 22s
build (Heltec_v3_companion_radio_ble)	1m 51s
build (LilyGo_Tlora_C6_repeater_)	1m 48s
	20m 1s

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