Implement batch inference for multi-apex

Use batch inference for efficiency

Edit:

> when we perform inference for multi-apex we essentially do a for loop
> ```python
> gpt_model, tokenizer = get_model_and_tokenizer(force_download, device=device)
> found_domains = set()
>
> for apex in sorted(domain_groups):
> found_domains |= _get_domains_for_group(...)
>
> return sorted(found_domains)
> ```
>
> Here we are not making use of batch inference, as in we don't batch different apex related subdomains simultaneously.