u256 not operator

[xunilrj]

Description

This PR is part of #4794. It implements the not operator for u256 and allows values bigger than u64.

To support that it implements U256 inside sway-types. For now, it is a bare minimum wrapper around BigUint. We may use fuel macro in the future, which implements all necessary functions.

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.