refactor: replace finalizer fiber with raw data pointer callback

Remove the dedicated finalizer fiber from WrenVM and change finalizer functions to accept a void* data pointer instead of a full WrenVM reference. This prevents user code from interacting with the VM during garbage collection, simplifying the GC path and eliminating the need for pre-allocated fiber infrastructure. Update the WrenForeignClassMethods struct, all built-in finalizers (file, test), and the binding/calling logic accordingly.

src/module/io.c

@@ -144,9 +144,9 @@ void fileAllocate(WrenVM* vm)
   *fd = (int)wrenGetSlotDouble(vm, 1);
 }
 
-void fileFinalize(WrenVM* vm)
+void fileFinalize(void* data)
 {
-  int fd = *(int*)wrenGetSlotForeign(vm, 0);
+  int fd = *(int*)data;
   
   // Already closed.
   if (fd == -1) return;