const-generics for enums

[xunilrj]

Description

This PR is part of #6860 and allows enums to have "const generics" like the code below:

enum E<T, const N: u64> {
    Nothing: (),
    Array: [T; N]
}

impl<T, const N: u64> E<T, N> {
    pub fn len_xxx2(self) -> u64 {
        N
    }
}

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).
  • If my change requires substantial documentation changes, I have requested support from the DevRel team
• 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.

[codspeed-hq]

CodSpeed Performance Report

Merging #7163 will not alter performance

_{Comparing xunilrj/enum-const-generics (5ac0724) with master (39251b6)}

Summary

✅ 22 untouched benchmarks

[IGI-111]

Can we also test a single variant enum or multiple const generic parameters?

[xunilrj]

Can we also test a single variant enum or multiple const generic parameters?

• Single variant enum: Done;
• Multiple const generic parameters: Not working on some cases. I have created an item in the umbrella issue for this case to deal with this later.