Add snapshot functionality to ink_sandbox

[0xLucca]

Summary

Closes #_

• [ n] y/n | Does it introduce breaking changes?
• [ y] y/n | Is it dependant on the specific version of cargo-contract or pallet-contracts?

Adds take_snapshot and restore_snapshot functionality to ink_sandbox

Description

Adds take_snapshot and restore_snapshot functionality to ink_sandbox

Checklist before requesting a review

• [y ] My code follows the style guidelines of this project
• [y ] I have added an entry to CHANGELOG.md
• [y] I have commented my code, particularly in hard-to-understand areas
• [y] I have added tests that prove my fix is effective or that my feature works
• [y] Any dependent changes have been merged and published in downstream modules

[cmichi]

@0xLucca Could you merge master into your branch?