feat: add basic reader and writer for keynote

[sparkybug]

Description

Summary

Added support for Apple IWork (Keynote) format in PHPPresentation with:

• New IWork reader/writer implementation
• Snappy compression support
• Protobuf message encoding/decoding
• Added google/protobuf dependency

Motivation

Enable PHPPresentation to work with Apple Keynote presentations, improving cross-platform compatibility.

Technical Changes

• Added compression and encoding utilities
• Implemented IWork format handlers
• Added format to IOFactory registry
• Includes test coverage

This change enables users to read and write Apple Keynote presentations while maintaining PHPPresentation's existing functionality.

Fixes #48
/claim #48

Checklist:

• My CI is 🟢
• I have covered by unit tests my new code (check build/coverage for coverage report)
• I have updated the documentation to describe the changes
• I have updated the changelog