ACE hangs or times out when processing EPUBs with very large package.opf manifest and spine

I have encountered an issue when processing an EPUB file using ACE where the tool hangs or runs indefinitely due to the size of the package.opf. The file contains:

- Over 20,000 items in the `` (`/package/manifest/item`)
- Over 1,600 `` entries in the (`/package/spine/itemref`)

While analyzing the code, I noticed that the issue seems to stem from the parseData function in `epub-parse.js` (specifically EpubParser.prototype.parseData). It appears that the time taken to process each `` in the `` increases significantly, eventually leading to timeouts or the validator running indefinitely.

This is blocking us from validating large-scale EPUB content using ACE.

Request:
Is there any known workaround or possible fix for this issue? Could ACE be improved to handle large EPUB files?

Inspect EpubParser.prototype.parseData in epub-parse.js and reproduce the slowdown with an EPUB containing very large manifest and spine entries. Profile the per-itemref processing to identify the scaling problem; done means ACE validates these large EPUBs without hanging or timing out.

Written by the indexing model from the issue text.