🧪 testing improvement: Add tests for csv module

[Tcode-Motion]

🎯 What: Added missing unit tests for the std.csv module registration and runtime functions (parse, stringify) in stdlib/src/csv.rs.
📊 Coverage: The new tests (test_csv_register, test_csv_parse, test_csv_stringify) cover the happy paths of module registration and execution of both exported functions.
✨ Result: Improved test coverage and reliability for the CSV standard library module, preventing future regressions.

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PR created automatically by Jules for task 1184424780295221576 started by @Tcode-Motion

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