Feature Request: Allow configuring `getImages` concurrency to avoid rate limit errors

[Jia-Yao]

I have a script that calls the components function from @figma-export/core but started seeing errors with status code 429 Too Many Requests recently due to Figma's new rate limits - https://developers.figma.com/docs/rest-api/rate-limits/

From code tracing, it looks like we end up calling the getImages function in packages/core/lib/figma.ts with a hardcoded concurrency limit of 30:

const getImages = async (...) => {
    const idss = chunk(ids, 200);
    const limit = pLimit(30);  // <-- hardcoded
    // ...
};

Since Figma's rate limits vary by seat/plan, this hardcoded value definitely doesn't work for all users. Please consider making it configurable, thanks!