Makes machine parts stackable, removes unused field in stack prototypes (#28434)

* Makes machine parts stacks, removes unused field in stack prototypes

* forgor

* Fix tests

* Fixes lathe construction. Yes. This sucks but there's no better way that doesnt involve refactoring machine parts completely

* detail

* a

Content.Server/Stack/StackSystem.cs

@@ -51,7 +51,7 @@ namespace Content.Server.Stack
 
             // Get a prototype ID to spawn the new entity. Null is also valid, although it should rarely be picked...
             var prototype = _prototypeManager.TryIndex<StackPrototype>(stack.StackTypeId, out var stackType)
-                ? stackType.Spawn
+                ? stackType.Spawn.ToString()
                 : Prototype(uid)?.ID;
 
             // Set the output parameter in the event instance to the newly split stack.