extract_outline_from_pdfium raises AttributeError on pypdfium2 4.x

### Bug

`extract_outline_from_pdfium()` in `docling/utils/pdf_outline.py` reads each bookmark
with `bm.get_title()` and `bm.get_dest()`. Those exist on pypdfium2 5, but on 4.30
`PdfDocument.get_toc()` yields a `PdfOutlineItem` namedtuple:

```python
PdfOutlineItem(level, title, is_closed, n_kids, page_index, view_mode, view_pos)
```

which has no such methods, so the call raises:

```
AttributeError: 'PdfOutlineItem' object has no attribute 'get_title'
```

`pyproject.toml` declares `pypdfium2>=4.30.0,!=4.30.1,<6.0.0`, so 4.x is a supported
range. On it, `PyPdfiumDocumentBackend.get_document_outline()` raises and the document
outline — the most authoritative heading-hierarchy signal — is unavailable.

The 4.30 namedtuple already carries what the 5 API reaches through the destination
object (`page_index`, `view_mode`, `view_pos`), so both shapes can be read.

### Steps to reproduce

```console
$ pip install 'pypdfium2==4.30.0'
```

```python
import pypdfium2 as pdfium
from docling.utils.pdf_outline import extract_outline_from_pdfium

# any PDF that has bookmarks
extract_outline_from_pdfium(pdfium.PdfDocument("manual.pdf"))
# AttributeError: 'PdfOutlineItem' object has no attribute 'get_title'
```

### Docling version

2.124.0

### Python version

3.13.15

Start in docling/utils/pdf_outline.py at extract_outline_from_pdfium(), then check the pypdfium2 version range in pyproject.toml. Reproduce with pypdfium2==4.30.0 and a PDF with bookmarks, then verify the function handles both the 4.x PdfOutlineItem shape and the 5.x API without raising an AttributeError.

Written by the indexing model from the issue text.