🧪 [testing improvement] Add missing test for module registration in csv.rs

[Tcode-Motion]

🎯 What: The register_csv() function in stdlib/src/csv.rs lacked a direct unit test to verify that the std.csv module is correctly instantiated and added to the StdlibRegistry with its required exports (parse, stringify).
📊 Coverage: The test covers the happy path of module registration in csv.rs. It verifies the module name, version, and presence of both the parse and stringify exported standard functions within the isolated test environment.
✨ Result: Increased unit test coverage and confidence in the standard library registry mechanism, ensuring that any future refactoring of StdlibRegistry or csv.rs will safely catch regressions.

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PR created automatically by Jules for task 4950216802809289615 started by @Tcode-Motion

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