fix: restore bookmark functionality

[pjtilsworth]

Resolves #2700

Other related PRs: #2715

Summary: All page bookmarks incorrectly referenced last page after PDFKit was upgraded and code refactored.
The faulty code refactoring applied the bookmarks at the end of the rendering, when the context is attached to the last page.
The fix is to attach bookmarks as the context changes rather than wait until the rendering is complete (and context lost).

I had suspected the issue was in PDFKit, but you can verify the PDFKit code works as expected by going to
the interactive browser provided in the libraries documentation and paste the following code provided below. The expectation is that clicking on a bookmark will take to that page.

var doc = new PDFDocument();
var stream = doc.pipe(blobStream());

// add first bookmark
doc.outline.addItem('bookmark page 1');
doc.text('Page 1',200, 50);

// draw some text
doc.addPage();
doc.outline.addItem('bookmark page 2');
doc.text('Page 2',200, 50);

doc.addPage();
doc.outline.addItem('bookmark page 3');
doc.text('Page 3',200, 50);

// end and display the document in the iframe to the right
doc.end();
stream.on('finish', function() {
  iframe.src = stream.toBlobURL('application/pdf');
});

[PoornakumarRasiraju]

Can we use index instead of i as this makes code more descriptive and improves readability?

[PoornakumarRasiraju]

use .toBe() instead of .toEqual() for string comparisons. .toBe() is faster and checks for strict equality with primitive values, whereas .toEqual() is used for deep equality checks on objects and arrays.