🧪 [Add unit test for word.rs module registration]

[Tcode-Motion]

🎯 What: The testing gap addressed is the lack of a unit test for the register_word function in stdlib/src/word.rs, which is responsible for registering the std.word module into the StdlibRegistry.
📊 Coverage: The test ensures that the register_word function behaves as expected on the happy path. It specifically verifies the registration mutates the StdlibRegistry to include a module named std.word with version 1.0.0 and empty exports and required_capabilities.
✨ Result: Test coverage for stdlib/src/word.rs module registration has been established and properly validates internal state mutations, improving the codebase's reliability and providing a safety net for future refactoring.

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PR created automatically by Jules for task 16961324647641374807 started by @Tcode-Motion

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