[Feature]: Feature Request: Add getPagesInfo() for bulk retrieval of page layout (view, rotate, userUnit) to reduce worker overhead

[insinfo]

Feature description

When building a custom viewer or handling documents with a large number of pages, it is often necessary to retrieve the dimensions and rotation of all pages upfront (e.g., to calculate the total scroll height or render a skeleton layout).

Currently, the only way to achieve this is by calling doc.getPage(i) sequentially for every page index. This requires N separate round-trips between the main thread and the PDF worker. For documents with hundreds of pages, the cumulative overhead of postMessage communication causes a significant performance bottleneck, often taking several seconds just to retrieve basic metadata (view, rotate, userUnit) that allows the UI to layout the document placeholders.

I propose adding a new method
getPagesInfo() to the PDFDocumentProxy API. This method would trigger a single message to the worker (GetPagesInfo), which iterates the page tree on the worker side and returns the layout data for all pages in a single response.
This eliminates the message-passing overhead and reduces the operation time from seconds to milliseconds for large documents.

I have implemented and tested this locally with the following changes:

1. src/core/worker.js (or pdf.worker.mjs build): Added a GetPagesInfo handler that resolves
   view, rotate, and userUnit for all pages efficiently.

handler.on("GetPagesInfo", function (data) {
  return pdfManager.ensureDoc("numPages").then(function (numPages) {
    const promises = [];
    for (let i = 0; i < numPages; i++) {
      promises.push(pdfManager.getPage(i).then(function (page) {
        return Promise.all([
          pdfManager.ensure(page, "view"),
          pdfManager.ensure(page, "rotate"),
          pdfManager.ensure(page, "userUnit")
        ]).then(function ([view, rotate, userUnit]) {
          return { view, rotate, userUnit };
        });
      }));
    }
    return Promise.all(promises);
  });
});

// In PDFDocumentProxy
getPagesInfo() {
  return this._transport.getPagesInfo();
}
// In WorkerTransport
getPagesInfo() {
  return this.messageHandler.sendWithPromise("GetPagesInfo", null);
}

This simple addition drastically improves the user experience for custom viewers dealing with long documents, allowing for instant "skeleton" rendering without blocking the UI or waiting for N asynchronous
getPage
calls.