Modernize codebase for latest dlib, numpy, and OpenCV compatibility

[ahitagnied]

Summary

• Added Python type hints to all main classes and methods for clarity and modern best practices.
• Removed unnecessary from __future__ import division imports (Python 3+).
• Added error handling for missing dlib model file in gaze_tracking.py.
• Unpinned dependency versions in requirements.txt to allow latest compatible versions.
• No changes to core logic or algorithms.

Motivation

These changes ensure compatibility with the latest versions of dlib, numpy, and OpenCV, and improve code readability and maintainability.

Testing

• All code runs with latest dependencies
• Demo runs successfully with python example.py