Adds constructible plastitanium reinforced walls (#92115)

## About The Pull Request

You can now construct reinforced plastitanium walls by using a single
plastitanium sheet on a reinforced girder. These are mostly identical to
syndicate walls, but only have 2 explosion resistance like normal
reinforced walls, as opposed to the 20 of syndicate walls.

## Why It's Good For The Game

Have you ever wanted a construction project to have that cool syndicate
aesthetic, but doing so would compromise its security due to the walls
being able to be simply welded down? Now you can make a syndicate
shuttle or satellite that will at least require thermite or the aid of
an engiborg to rapidly break into.

## Changelog

🆑
add: You can construct reinforced plastitanium walls by using
plastitanium on reinforced girders.
/🆑

code/game/objects/structures/girders.dm

@@ -230,9 +230,25 @@
 					qdel(src)
 				return
 
+		if(istype(sheets, /obj/item/stack/sheet/mineral/plastitanium))
+			if(state == GIRDER_REINF)
+				if(sheets.get_amount() < 1)
+					return
+				balloon_alert(user, "adding plating...")
+				if(do_after(user, 50*platingmodifier, target = src))
+					if(sheets.get_amount() < 1)
+						return
+					sheets.use(1)
+					var/turf/T = get_turf(src)
+					T.place_on_top(/turf/closed/wall/r_wall/plastitanium)
+					transfer_fingerprints_to(T)
+					qdel(src)
+				return
+			// No return here because generic material construction handles making normal plastitanium walls
+
 		if(!sheets.has_unique_girder && sheets.material_type)
 			if(istype(src, /obj/structure/girder/reinforced))
-				balloon_alert(user, "need plasteel!")
+				balloon_alert(user, "need plasteel or plastitanium!")
 				return
 			var/M = sheets.sheettype
 			var/amount = construction_cost["exotic_material"]