lib: Updated __cmp__ method for Python3 functionality

[arohanajit]

wrt to #1809 This PR updates the __cmp__ method in saferef.py to be compatible with Python 3. Comparison methods __eq__ and __lt__ are implemented to maintain the same functionality without requiring changes elsewhere in the code.

Changes:

• Added __eq__ method for equality comparison.
• Added __lt__ method for less-than comparison.
• The __cmp__ method now uses the rich comparison methods for its logic.

This shouldn't change overall behavior of saferef class.

[petrasovaa]

@echoix any suggestions here? Upstream has no fix for it. It's not used.

[echoix]

@echoix any suggestions here? Upstream has no fix for it. It's not used.

I'd need to have a deep look for this, as it might be impactful. I think we needed to revert one of my PRs that touched this if I remember well.

I'd be cautious and read well. Was it @wenzeslaus that has experience with this file?