Shadow DOM list false positive

### Product

axe-core

### Product Version

4.11.1

### Latest Version

- [x] I have tested the issue with the latest version of the product

### Issue Description

#### Expectation
When a `

` or `
` element uses a `` to distribute custom elements whose shadow DOM renders as `
1. `, the list rule should pass. The structure is semantically valid — each custom element is a web component wrapper around an `
2. `.

   #### Actual
   The list rule fails with a violation on the `

   `, reporting that it contains non-`
   • ` children. This is a false positive caused by axe-core evaluating the slotted custom elements (``) as the direct children of `
     ` in the flat tree, without looking through their shadow DOM to see that they render as `
     • `.

       #### How to Reproduce
       https://codepen.io/lupecamacho/pen/pvEgQPj

       Or the following minimal example:

       ```html

       
       One
       Two
       Three
       
       ```

       ```js
       import { LitElement, html } from "https://cdn.skypack.dev/lit";

       class MyList extends LitElement {
       render() {
       return html`

       `;
       }
       }

       class MyListItem extends LitElement {
       render() {
       return html`

     `;
     }
     }

     customElements.define("my-list", MyList);
     customElements.define("my-list-item", MyListItem);
     ```
     Running `axe.run()` reports a list violation on the `

     ` element inside ``'s shadow DOM.

     #### Additional context

     The issue is in the only-listitems check (lib/checks/lists/only-listitems-evaluate.js). axe-core's flat tree algorithm correctly resolves the `` in `

     `, making the `` elements the virtual children of `
     `. However, the check only tests whether each child is literally an `
     • ` element or has an explicit listitem role — it does not account for the case where the child is a shadow host whose shadow DOM root element is an `
     • `.

       The same pattern applies to any web component that encapsulates list item semantics in a shadow DOM (e.g. design system components).
       

Start by reading lib/checks/lists/only-listitems-evaluate.js and reproduce the report with the linked CodePen or the minimal LitElement example using axe.run(). The fix is done when a ul or ol containing slotted custom elements whose shadow DOM renders li no longer reports a list violation, while ordinary invalid children remain detected.

Written by the indexing model from the issue text.