Add optional_rect and required_rect dictionary readers

[Velli20]

Summary

• Add Dictionary::optional_rect(key, objects) and Dictionary::required_rect(key, objects) to read a four-number array entry as a Rect, keeping the original coordinate order.
• Use them for /CropBox (document and page) and /RD (annotation subtypes), and build optional_bbox, required_bbox and optional_media_box on top of them. Behavior is unchanged.
• /Domain in function shadings stays an optional_array_of::<f32, 4> read: it is [xmin xmax ymin ymax], not a rectangle.

Testing

• cargo clippy --all --workspace, cargo fmt --check
• cargo test -p pdf-object-reader -p pdf-document -p pdf-annotation-core

🤖 Generated with Claude Code

[github-actions]

Conformance reads

Documents that Safe-PDF reads differently from the base commit, compared with PDFium. A read
regresses when Safe-PDF fails to open a document it opened before, crashes or times out, or
counts a different number of pages than PDFium.

pdf.js corpus

1008 documents compared with b469ecf: 1 read worse, 0 read better.

Regressions

Document	Base	This pull request
issue17190_1	read, 1 page	timeout: time limit exceeded (stage safe-read)

840 documents of the PDFium corpus read as on b469ecf.

Details are in the job summaries of the workflow run. Rerun a case locally with
cargo conformance run --corpus <corpus> --read-only --case <id>.