Greentext antag datum and OnRoundend hook. (#35584)

* Greentext antag datum and OnRoundend hook.

* review stuff

code/controllers/subsystem/ticker.dm

@@ -61,6 +61,7 @@ SUBSYSTEM_DEF(ticker)
 
 	var/round_start_time = 0
 	var/list/round_start_events
+	var/list/round_end_events
 	var/mode_result = "undefined"
 	var/end_state = "undefined"
 
@@ -336,12 +337,20 @@ SUBSYSTEM_DEF(ticker)
 	send2irc("Server", "Round [GLOB.round_id ? "#[GLOB.round_id]:" : "of"] [hide_mode ? "secret":"[mode.name]"] has started[allmins.len ? ".":" with no active admins online!"]")
 	setup_done = TRUE
 
+//These callbacks will fire after roundstart key transfer
 /datum/controller/subsystem/ticker/proc/OnRoundstart(datum/callback/cb)
 	if(!HasRoundStarted())
 		LAZYADD(round_start_events, cb)
 	else
 		cb.InvokeAsync()
 
+//These callbacks will fire before roundend report
+/datum/controller/subsystem/ticker/proc/OnRoundend(datum/callback/cb)
+	if(current_state >= GAME_STATE_FINISHED)
+		cb.InvokeAsync()
+	else
+		LAZYADD(round_end_events, cb)
+
 /datum/controller/subsystem/ticker/proc/station_explosion_detonation(atom/bomb)
 	if(bomb)	//BOOM
 		var/turf/epi = bomb.loc