add Clone method to StarkProof

[ShuangWu121]

Description:
This PR adds a Clone implementation for StarkProof. In my current project, I need the ability to duplicate StarkProof instances to simplify reuse in scenarios where moving it once isn’t sufficient. Specifically, I am implementing a prover and want to check the proof as a sanity check inside prover before actually sending the proof to my verifier.

Uncertainty:
I haven’t identified a specific reason why Clone wasn’t implemented initially, and I recognize there might be design considerations or resource management concerns behind that choice. There are potential issues or constraints I might have missed.

Request:
If adding Clone is acceptable within the project’s design, this small change could improve usability for cases like mine. However, if Clone is not desired for any reason, I’m open to finding alternative approaches to handle this in my project—though having Clone would definitely make things easier! 😊

[reviewable-StarkWare]

This change is