Generation of pdf is too slow for large html

I am now using version 1.0.2, but the pdf build is still hang.
The size of html is 13241929
I have tried many times and increased the heap size to 4G.
My running machine is i5 4460, 16G RAM.

Attafched with the test html
[test.txt](https://github.com/danfickle/openhtmltopdf/files/4752989/test.txt)

My code for pdf generation is as follow:

```
public byte[] generateFromHtml(String html) throws Exception {
try (ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream()) {
PdfRendererBuilder builder = new PdfRendererBuilder();
builder.useFont(getFont(PMingLiU), "PMingLiU");
builder.useFont(getFont(PMingLiUExtB), "PMingLiU-ExtB");
builder.useFont(getFont(seguiemj), "Segoe UI Emoji");
builder.withHtmlContent(html, null);
builder.useFastMode();
builder.toStream(byteArrayOutputStream);
builder.run();
return byteArrayOutputStream.toByteArray();
}
}
```

_Originally posted by @Infinity821 in https://github.com/danfickle/openhtmltopdf/issues/180#issuecomment-640995477_

Begin with the attached test.txt and the generateFromHtml entry point, then reproduce the PDF build using the reported 13241929-size HTML and current heap settings. Done means identifying a reproducible bottleneck in PdfRendererBuilder or the generation path and documenting a measurable improvement for large HTML inputs.

Written by the indexing model from the issue text.