return type checked trait constraints

[xunilrj]

Description

This PR fixes #6382.

The issue was that TypeParameter::type_check_trait_constraints(...) mutates the type inside the TypeEngine, but it was not returning the new type-checked trait constraints.

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 #6604 will not alter performance

_{Comparing xunilrj/fix-trait-constraint-type-check (0011fcf) with master (759bb9e)}

Summary

✅ 22 untouched benchmarks

[IGI-111]

Can we add a test for this?

[xunilrj]

Can we add a test for this?

Done.