Upgrade python to V3

[nem-c]

Description:
Python 2 reached its official end-of-life on January 1, 2020, and is no longer receiving security updates or bug fixes. To ensure long-term maintainability, compatibility, and security, we should migrate the project to Python 3.

Benefits:

• Continued support and compatibility with modern libraries and frameworks.
• Access to performance improvements and new language features in Python 3.
• Compliance with community standards and supported environments.

Tasks:

1. Update requirements.txt or dependency files to ensure compatibility with Python 3.
2. Replace deprecated Python 2 syntax (e.g., print statements, exception handling).
3. Update string handling (unicode vs str, bytes) where necessary.
4. Ensure all tests run successfully under Python 3.

Additional Notes:

• Backward compatibility with Python 2 will not be maintained.

[nem-c]

PR available here #548