🧹 [refactor] Extract logic from execute_statement to improve readability

[Tcode-Motion]

🎯 What: The execute_statement function in runtime/interpreter/src/statements.rs had an excessively long match block handling numerous complex statements directly inline, harming readability.
💡 Why: Extracting the logic into well-named private helper methods (execute_if_stmt, execute_while_stmt, etc.) slims down the dispatch function and dramatically improves readability and maintainability without altering runtime behavior.
✅ Verification: Verified via cargo check and successfully ran cargo test -p techscript_interpreter as well as the full cargo test --workspace suite to confirm that there are no regressions.
✨ Result: The execute_statement method is now clean and concise, and the internal complexity is properly modularized.

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PR created automatically by Jules for task 4472496660871606817 started by @Tcode-Motion

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