Add test_cycle_detection_in_page_tree to verify that circular references
in the /Pages tree are detected and handled gracefully without panicking.
The test creates a page tree with a cycle (parent -> child1 -> child2 -> child1)
and verifies that the flattener returns the valid pages while pruning the
cyclic portion.
Acceptance criteria verified:
- 3-level /Pages inheritance with MediaBox: PASS
- EC-09 missing MediaBox defaults to US Letter: PASS
- /Pages tree with cycles detected: PASS
- /Rotate value 45 clamped to 0: PASS
- Page count validation: PASS
- proptest random shapes never panic: PASS
- INV-8 no panics on invalid input: PASS
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Bead-Id: pdftract-5tmcg
Bead-Id: pdftract-4iier
