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 degrade performances by 37.49%

_{Comparing xunilrj/fix-trait-constraint-type-check (5af5b52) with master (d399580)}

Summary

❌ 1 regressions
✅ 21 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	master	xunilrj/fix-trait-constraint-type-check	Change
❌	prepare_rename	1.6 ms	2.5 ms	-37.49%