Mining RFD can now make train engine and carts (#19235)

Improved / refactored some code, particularly around RFD.
Added the ability for mining RFD to build the mining train engine and
carts.
Removed the RFD, carts and engine from the mining vendor.
Added the RFD as a roundstart printable protolathe design.
Made the mining vendor list a GLOB variable.
Resolved a runtime on vehicles trying to turn on without a cell being
present.
Mining vendor pizzas now have a random pizza subtype.

code/modules/vehicles/cargo_train.dm

@@ -6,7 +6,8 @@
 		- ALT-click the truck to remove the key from the ignition.<br>\
 		- Click the truck to open a UI menu.<br>\
 		- Click the resist button or type \"resist\" in the command bar at the bottom of your screen to get off the truck.<br>\
-		- If latched, you can use a wrench to unlatch."
+		- If latched, you can use a wrench to unlatch.<br>\
+		- Click-drag on a trolley to latch and tow it."
 	icon = 'icons/obj/vehicles.dmi'
 	icon_state = "cargo_engine"
 	on = 0
@@ -33,7 +34,7 @@
 
 /obj/vehicle/train/cargo/trolley
 	name = "cargo train trolley"
-	desc_info = "You can use a wrench to unlatch this."
+	desc_info = "You can use a wrench to unlatch this, click-drag to link it to another trolley to tow."
 	icon = 'icons/obj/vehicles.dmi'
 	icon_state = "cargo_trailer"
 	anchored = 0
@@ -242,6 +243,10 @@
 
 	if(is_train_head())
 		if(direction == reverse_direction(dir) && tow)
+			//Allow the engine to rotate, but only if there's not another piece in the new direction
+			//Basically, to allow the first rotation at spawn to align with the rest of the convoy, without it being a CBT
+			if(!(locate(/obj/vehicle/train) in get_step(src, direction)))
+				set_dir(direction)
 			return 0
 		if(Move(get_step(src, direction)))
 			return 1
@@ -277,6 +282,10 @@
 		if("Toggle Latching")
 			if(tow)
 				tow.unattach(user)
+			else
+				var/obj/vehicle/train/cargo/trolley/nearby_trolley = locate() in orange(src, 1)
+				if(nearby_trolley)
+					src.latch(nearby_trolley)
 
 /obj/vehicle/train/cargo/engine/AltClick(var/mob/user)
 	if(Adjacent(user))

code/modules/vehicles/vehicle.dm

@@ -191,16 +191,16 @@
 //-------------------------------------------
 /obj/vehicle/proc/turn_on()
 	if(stat)
-		return 0
-	if(powered && cell.charge < charge_use && !organic)
-		return 0
-	on = 1
+		return FALSE
+	if(powered && cell?.charge < charge_use && !organic)
+		return FALSE
+	on = TRUE
 	set_light(initial(light_range))
 	update_icon()
-	return 1
+	return TRUE
 
 /obj/vehicle/proc/turn_off()
-	on = 0
+	on = FALSE
 	set_light(0)
 	update_icon()
 
@@ -297,49 +297,56 @@
 // the vehicle load() definition before
 // calling this parent proc.
 //-------------------------------------------
-/obj/vehicle/proc/load(var/atom/movable/C)
+/**
+ * Loads an /atom onto the vehicle
+ *
+ * * thing_to_load - The thing to load, an `/obj` or `/mob`
+ *
+ * Returns `TRUE` if the load was successful, `FALSE` otherwise
+ */
+/obj/vehicle/proc/load(var/atom/movable/thing_to_load)
 	//This loads objects onto the vehicle so they can still be interacted with.
 	//Define allowed items for loading in specific vehicle definitions.
-	if(!isturf(C.loc)) //To prevent loading things from someone's inventory, which wouldn't get handled properly.
-		return 0
-	if(load || C.anchored)
-		return 0
+	if(!isturf(thing_to_load.loc)) //To prevent loading things from someone's inventory, which wouldn't get handled properly.
+		return FALSE
+	if(load || thing_to_load.anchored)
+		return FALSE
 
 	// if a crate/closet, close before loading
-	var/obj/structure/closet/closet = C
+	var/obj/structure/closet/closet = thing_to_load
 	if(istype(closet))
 		closet.close()
 
-	C.forceMove(loc)
-	C.set_dir(dir)
-	C.anchored = 1
+	thing_to_load.forceMove(loc)
+	thing_to_load.set_dir(dir)
+	thing_to_load.anchored = TRUE
 
-	load = C
+	load = thing_to_load
 
-	C.layer = VEHICLE_LOAD_LAYER
+	thing_to_load.layer = VEHICLE_LOAD_LAYER
 	if(load_item_visible)
-		C.pixel_x += load_offset_x
-		if(ismob(C))
-			C.pixel_y += mob_offset_y
+		thing_to_load.pixel_x += load_offset_x
+		if(ismob(thing_to_load))
+			thing_to_load.pixel_y += mob_offset_y
 		else
-			if(istype(C, /obj/structure/closet/crate))
-				C.pixel_y += load_offset_y
+			if(istype(thing_to_load, /obj/structure/closet/crate))
+				thing_to_load.pixel_y += load_offset_y
 			else
-				C.pixel_y += 10
+				thing_to_load.pixel_y += 10
 
-	if(ismob(C))
-		buckle(C, C)
+	if(ismob(thing_to_load))
+		buckle(thing_to_load, thing_to_load)
 
-	return 1
+	return TRUE
 
-/obj/vehicle/buckle(var/atom/movable/C, mob/user)
+/obj/vehicle/buckle(atom/movable/buckling_atom, mob/user)
 	. = ..()
 	if(. && buckling_sound)
 		playsound(src, buckling_sound, 20)
 
-/obj/vehicle/user_unbuckle(var/mob/user, var/direction)
+/obj/vehicle/user_unbuckle(mob/user)
 	..()
-	unload(user, direction)
+	unload(user)
 	return
 
 /obj/vehicle/proc/unload(var/mob/user, var/direction)