Pillow: Unbounded recursion parsing a PDF page tree or trailer chain (incomplete fix for CVE-2026-42310)

Summary When an application appends to an existing PDF with Image.save..., format="PDF", append=True, Pillow parses that file with PdfParser. Two recursive parsers have no effective bound. linearizepagetree follows /Kids with no visited set or depth limit, so a cyclic or duplicated page tree...