Support AFP document format

### Requested feature
Add support for AFP (Advanced Function Presentation) documents to the library’s document handling pipeline. AFP is an IBM-origin printer/document architecture commonly used in enterprise environments (e.g., statements, invoices, and batch-generated reports). Users need to open, inspect, extract, and convert AFP content similarly to how the library already supports formats like PDF/TIFF.
User needs
Not
- Import AFP files and obtain a normalized document model (pages, resources, text, images).
- Extract text (including positioning, fonts), images, and metadata.
- Convert AFP to one or more target formats (e.g., PDF or image per page) for downstream processing, preview, or archiving.
- Handle common AFP resources: MO:DCA-P structured fields, page segments, overlays, fonts (outline/raster), and images (e.g., IOCA).

### Alternatives
Use an external AFP-to-PDF converter as a preprocessing step, then feed PDF into the library.

- Pros: Faster to adopt; leverages mature tools.
- Cons: Adds external dependency, potential licensing issues, and may lose structured text data.