Improve and Modernize setup.py for Rememberer Package

[Sania1125]

Summary

• Refactored setup.py for better structure and clarity.
• Updated description, keywords, and project URLs.
• Added classifiers for better PyPI metadata.
• Made install requirements conditional for different Python versions (pickle5 only if Python < 3.8).

Why?

These changes make the project easier to install, easier to find, and more professional for future publishing.

✅ No breaking changes.
✅ Backward compatible.

Thanks for reviewing!