🧹 [Extract standard library Sys registry exports]

[Tcode-Motion]

🎯 What: Extracted inline closure callbacks for standard library system exports (std.fs and std.time) into separate, standalone functions in stdlib/src/sys.rs.
💡 Why: Reduces massive setup boilerplate inside the StdlibRegistry implementation and clearly separates the security capability checks from the function registration scaffolding, improving code maintainability and readability.
✅ Verification: Ran workspace tests (cargo test --workspace) successfully to ensure no regressions were introduced to standard library functionality. Visual code review confirmed safe refactoring.
✨ Result: A cleaner register_sys method with distinct function definitions that are easier to test and modify individually in the future.

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PR created automatically by Jules for task 6512869720815095444 started by @Tcode-Motion

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