Add compatibility wrapper classes for PdfFileWriter/PdfFileReader
to support both PyPDF2 2.x and 3.x versions.
Changes:
- Add PyPDF2 compatibility classes in snailmail/models/snailmail_letter.py
- Create comprehensive documentation in doc/PATCH_PDFWRITER.md
- Support for addPage, appendPagesFromReader, and getPage methods
Resolves PyPDF2.errors.DeprecationError: PdfFileWriter is deprecated
and was removed in PyPDF2 3.0.0.
🤖 assisted by claude
