🧹 Extract import lowering to reduce deep nesting in lower_statement

[Tcode-Motion]

🎯 What: Reduced deep nesting in the lower_statement method within compiler/ir/src/lowering.rs by extracting the Statement::Import match arm logic into a new dedicated lower_import method.

💡 Why: The lower_statement function was growing overly large and deeply nested, specifically around the Statement::Import handling which accounted for roughly 70 lines of complex control flow. Extracting this into a separate method improves readability, makes the lower_statement match block more consistent with other statement types (like lower_var_decl and lower_const_decl), and makes the codebase easier to maintain.

✅ Verification:

• Ran targeted tests for the IR compiler (cargo test -p techscript_ir).
• Ran the full workspace test suite (cargo test --workspace) to ensure no regressions were introduced elsewhere.
• Ran formatting (cargo fmt --all).
• Requested and passed code review.

✨ Result: The lower_statement method is now significantly shorter and easier to read, with the complex import lowering logic cleanly isolated in lower_import without changing any behavior.

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PR created automatically by Jules for task 10670054220632445716 started by @Tcode-Motion

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