🧹 [code health] Refactor lower_statement to use specific lowering methods

[Tcode-Motion]

🎯 What: Extracted the large blocks of logic for lowering If, While, For, Repeat, and Try statements from lower_statement into their own private methods (lower_if, lower_while, lower_for, lower_repeat, lower_try).
💡 Why: The lower_statement function was excessively long and complex, making it difficult to read and maintain. Moving the logic into statement-specific methods greatly improves readability and encapsulation.
✅ Verification: I confirmed that this refactoring is purely structural and does not change any semantics. I ran cargo test -p techscript_ir which passed, and then executed the full workspace checks (cargo check --workspace, cargo test --workspace, cargo fmt --all -- --check, cargo clippy --workspace --all-targets -- -D warnings), all of which passed successfully.
✨ Result: The lower_statement function is now much cleaner and easier to navigate, enhancing overall code health and maintainability.

---

PR created automatically by Jules for task 8211447227162523621 started by @Tcode-Motion

[google-labs-jules]

👋 Jules, reporting for duty! I'm here to lend a hand with this pull request.

When you start a review, I'll add a 👀 emoji to each comment to let you know I've read it. I'll focus on feedback directed at me and will do my best to stay out of conversations between you and other bots or reviewers to keep the noise down.

I'll push a commit with your requested changes shortly after. Please note there might be a delay between these steps, but rest assured I'm on the job!

For more direct control, you can switch me to Reactive Mode. When this mode is on, I will only act on comments where you specifically mention me with @jules. You can find this option in the Pull Request section of your global Jules UI settings. You can always switch back!

New to Jules? Learn more at jules.google/docs.

---

For security, I will only act on instructions from the user who triggered this task.