Split the 1288-line info.py into smaller, single-responsibility modules:
- _types.py: Enums, type aliases, lookup dictionaries
- _contentstream.py: PDF content stream parsing, DPI calculation
- _image.py: ImageInfo class and image finding functions
- _worker.py: Concurrency/worker process handling
- info.py: PageInfo, PdfInfo classes (reduced to ~530 lines)
Public API unchanged - all existing imports continue to work.