Refactor typed/parsed AST

[tritao]

Description

Refactors the parsed and typed AST so let/use/mod statements are first-class nodes, and rewires the compiler, IR generator, and tooling around the new typed statement representation.

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 #7441 will not alter performance

_{Comparing tritao:refactor-typed-ast (a1a3e00) with master (ca96726)}

Summary

✅ 25 untouched