How can I create a list of unique class instances for an object?

Contributing to Blender
,
1

I am working on a project that requires each object to have a list of custom class instances, so that I can get and set things from the list as needed.

I tried to do something like this (the code is on the end of the topic), but it gave me the following error when I tried to run the add_to_list operator: TypeError: only floats, ints and dicts are allowed in ID property arrays
I guess I should find a way to change it to another type, like CollectionProperty, but I couldn’t do it.

I would appreciate it if you could help me.
Code (all registration is done outside these scripts automatically and surely):

script 1:

class list_item:
     global_list_id = "list_id"

     name: bpy.props.StringProperty()
     texture: bpy.props.PointerProperty(type=bpy.types.Image)

     def __init__(self, name, texture):
         self.name = name
         self.texture = texture

     @staticmethod
     def get_or_create_list(obj, context):
         if list_item.global_list_id not in obj:
             obj[list_item.global_list_id] = []
         return obj[list_item.global_list_id]
    
     @staticmethod
     def append_to_object(obj: bpy.types.Object, append, context: bpy.context):
         items_list = list_item.get_or_create_list(obj, context)
         items_list.append(append)
         obj(list_item.global_list_id] = items_list
         return list_item.get_or_create_list(obj, context)

script 2:

import bpy
from ..utility.list_item import list_item


class add_to_list_operator(bpy.types.Operator):
     bl_idname = "addon.add_to_list"
    
     item_name : bpy.props.StringProperty(name="Name", default="New Item")

     def execute(self, context):
         obj = context.active_object
         print(f"Operator executed with args: {self.item_name}")

         new_image = bpy.data.images.new(name=self.texture_name, width=1920, height=1080)

         new_item = list_item(self.texture_name, new_image)
         list_item.append_to_object(obj=obj, append=new_item, context=context)

         return {'FINISHED'}