pdfdelta adds visual diffs for PDFs

This is a deceptively useful tool: it solves the “what actually changed on the page?” problem without forcing reviewers to eyeball two PDFs side by side.

• –Keeps changes anchored to the original page layout, which makes reviews faster than text-only comparisons
• –Handles multi-column papers and tries to ignore reflow noise from line wraps, paragraph breaks, and page breaks
• –The native annotation approach should be especially helpful for researchers, editors, and technical writers
• –Open-source Python packaging plus a simple CLI lowers the friction for quick document checks