Asynchronous rendering of a custom blot

[paleo]

I needed to render a blot asynchronously. So I created a duplicated version of the converter (QuillDeltaToHtmlAsyncConverter) for asynchronous rendering.

Example:

import { QuillDeltaToHtmlAsyncConverter } from 'quill-delta-to-html'; 

const converter = new QuillDeltaToHtmlAsyncConverter(ops);

converter.renderCustomWith(async function(customOp, contextOp) {
    await // …
    return `<span id="${val.id}">${val.text}</span>`;
});

const html = await converter.convert();

@nozer Would you be interested if I refreshed your code? In this PR, I duplicated the code because it is old and I wasn't comfortable with refactoring. But here's what I plan to do in a second PR:

• Upgrade all the dependencies
• Lint with Biome
• Test with Jest or Vitest
• Use modern JS/TS (no var, etc.)
• Remove the compiled files
• If possible, rewrite the code in a way that async an sync code is written once (probably with functions & objects instead of classes)