pAIs and lightgeists can now correctly climb ladders. (#70869)

## About The Pull Request
See the title and the relative issue reports.

The logic here is that, if they can move, chances are they can also use
ladders (with a few exceptions such as camera mobs). This ought to
include both pAIs and lightgeists, even if they cannot directly interact
with about every other object in the game.

I have also moved lightgeists onto a new file, from colossus.dm.

## Why It's Good For The Game
This will fix #57061 and fix #69228.

## Changelog

🆑
fix: pAIs and lightgeists can now correctly climb ladders.
fix: fixed a small issue with the radial menu for ladders that caused
the user to travel down when abruptly closed.
/🆑

Co-authored-by: Mothblocks <35135081+Mothblocks@users.noreply.github.com>

code/game/objects/structures/ladders.dm

@@ -157,7 +157,7 @@
 			going_up = TRUE
 		if("Down")
 			going_up = FALSE
-		if("Cancel")
+		else
 			return
 
 	if(is_ghost || !travel_time)
@@ -251,7 +251,18 @@
 /obj/structure/ladder/attack_robot_secondary(mob/living/silicon/robot/user)
 	. = ..()
 	if(. == SECONDARY_ATTACK_CANCEL_ATTACK_CHAIN || !user.Adjacent(src))
-		return SECONDARY_ATTACK_CONTINUE_CHAIN
+		return
+	use(user, going_up = FALSE)
+	return SECONDARY_ATTACK_CANCEL_ATTACK_CHAIN
+
+/obj/structure/ladder/attack_pai(mob/user, list/modifiers)
+	use(user)
+	return TRUE
+
+/obj/structure/ladder/attack_pai_secondary(mob/user, list/modifiers)
+	. = ..()
+	if(. == SECONDARY_ATTACK_CANCEL_ATTACK_CHAIN)
+		return
 	use(user, going_up = FALSE)
 	return SECONDARY_ATTACK_CANCEL_ATTACK_CHAIN