u256: log, log2 and sqrt impl (#5329)

[sudhackar]

Description

simple changes that borrows on u128 implementations of log, log2 and sqrt - only with little changes. Have added a test on u128 too as it was missing for log and the output was confusing to at least me.

This should fix #5329

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.

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[sudhackar]

ping @SwayStar123 as requested

[SwayStar123]

Thank you for the PR! But it looks like you added the functions to the wrong type. the u256 library houses the deprecated U256 type. There is now a primitive u256 type, it needs the implementation in the math library https://github.com/FuelLabs/sway/blob/master/sway-lib-std/src/math.sw

[sudhackar]

oof. my bad. Let me do that.

Should I scrub off these changes too?

[SwayStar123]

Yes please remove the changes related to the deprecated structs. As they will eventually be removed entirely, they are only preserved currently to give time for teams to migrate to the primitive type