fix: enable module loading for custom extensions

[CodeWithKyrian]

Currently, the package loads custom extension scripts as regular JavaScript files, which prevents the use of ES module syntax (import statements). This means even the example snippet in the docs will not work, nor will using extensions from packages like @tiptap-pro, be very straighforward to use

import Hero from "./hero.js";
window.TiptapEditorExtensions = {
    hero: [Hero]
}

This code fails with Uncaught SyntaxError: Cannot use import statement outside a module.

This PR modifies the asset registration to load custom extension scripts as modules by using Filament's module() method, allowing one to use ES module syntax in their extension scripts

[awcodes]

Custom extensions should go through a build process. Using modules in this context is not going to work in production without having all the imports publicly accessible, which doesn't make sense to me, especially when trying to use tiptap pro extensions that would live in node_modules and not be accessible via a url route.