fix(CVSS2, CVSS3, CVSS4): implement and correct __eq__ methods

[fqlenos]

This PR addresses the following:

• Implement the missing __eq__ method in the CVSS4 class, which was necessary to enable proper object comparison. Without this, comparing two CVSS4 objects would not work correctly.
• Correct and refactor the __eq__ methods in CVSS2 and CVSS3 to ensure consistency across all CVSS classes.

These changes resolve issues with object comparisons and ensure that all CVSS classes now follow consistent behavior when comparing instances.

[jsvob]

Hi @fqlenos ! Thank you for your contribution.

Why the changes from return NotImplemented to return False, please? I admit I've never implemented comparison, but don't have the spare cycles now to explore it fully.

[fqlenos]

Hello @jsvob!

The change was made for the following reasons:

1. Behavioral consistency: return False directly communicates that the comparison failed, which I think aligns with the expected behavior when comparing two instances.
2. Reverse comparison: return NotImplemented signals Python to try other comparison method, such as the reverse comparison (o.clean_vector() == self.clean_vector()) if available.
3. Practical impact: return False is clearer in contexts where comparisons are used directly, such as if CVSS3(...) == CVSS3(...): .... Using return NotImplemented would delegate comparison to other __eq__ method, which could lead to unexpected behavior if not handled correctly.

In short, and in my opinion, returning False here simplifies and ensures a clear outcome when two objects are not equal or are of different types, without relying on additional fallback logic.

[jsvob]

Thank you for the detailed explanation and fix, @fqlenos !