adds swapping pens in PDAs (#84437)

## About The Pull Request

Added the ability to swap items in PDAs


<details>
<summary>Videos</summary>


https://github.com/tgstation/tgstation/assets/112967882/b3c63d7b-7913-42a6-83e7-d2989cdac8b2

</details>

## Why It's Good For The Game

You can quickly change items stored in the PDA slots without doing
unnecessary actions (pulling the pen out of the PDA, removing it, and
inserting another pen)
## Changelog
🆑
qol: you can now swap pens in pdas
/🆑

---------

Co-authored-by: Ghom <42542238+Ghommie@users.noreply.github.com>

code/modules/modular_computers/computers/item/pda.dm

@@ -149,14 +149,14 @@
 	if(tool.w_class >= WEIGHT_CLASS_SMALL) // Anything equal to or larger than small won't work
 		user.balloon_alert(user, "too big!")
 		return ITEM_INTERACT_BLOCKING
-	if(inserted_item)
-		balloon_alert(user, "no room!")
-		return ITEM_INTERACT_BLOCKING
 	if(!user.transferItemToLoc(tool, src))
 		return ITEM_INTERACT_BLOCKING
-	balloon_alert(user, "inserted [tool]")
-	inserted_item = tool
-	playsound(src, 'sound/machines/pda_button1.ogg', 50, TRUE)
+	if(inserted_item)
+		swap_pen(user, tool)
+	else
+		balloon_alert(user, "inserted [tool]")
+		inserted_item = tool
+		playsound(src, 'sound/machines/pda_button1.ogg', 50, TRUE)
 	return ITEM_INTERACT_SUCCESS
 
 
@@ -185,6 +185,14 @@
 		update_appearance()
 		playsound(src, 'sound/machines/pda_button2.ogg', 50, TRUE)
 
+/obj/item/modular_computer/pda/proc/swap_pen(mob/user, obj/item/tool)
+	if(inserted_item)
+		balloon_alert(user, "swapped pens")
+		user.put_in_hands(inserted_item)
+		inserted_item = tool
+		update_appearance()
+		playsound(src, 'sound/machines/pda_button1.ogg', 50, TRUE)
+
 /obj/item/modular_computer/pda/proc/explode(mob/target, mob/bomber, from_message_menu = FALSE)
 	var/turf/current_turf = get_turf(src)