Replace radio frequency magic numbers with defines (#33236)

* Change transmission_method to use defines rather than magic numbers

* Use MIN and MAX_FREE_FREQ defines when bounds-checking radios

* Remove violently broken "Debug Signals" verb

The relevant Destroy() is never called, making the static pointers list
take lots of memory and be large enough, even at roundstart, to crash
the chat when invoked (25k+ entries).

* Remove unnecessary checks for SSradio not existing

* Move department frequencies from GLOB to defines

* Replace all hardcoded radio frequencies with named defines

* Change the radio filters to be defines

* Use a define for the default signaler code

code/game/gamemodes/nuclear/nuclear.dm

@@ -150,8 +150,8 @@
 
 /datum/outfit/syndicate/post_equip(mob/living/carbon/human/H)
 	var/obj/item/device/radio/R = H.ears
-	R.set_frequency(GLOB.SYND_FREQ)
-	R.freqlock = 1
+	R.set_frequency(FREQ_SYNDICATE)
+	R.freqlock = TRUE
 	if(command_radio)
 		R.command = TRUE