[Tests] Replace mocks with behavior-based testing in fs.test.ts

[gonzaloriestra]

WHY are these changes introduced?

The current test suite in packages/cli-kit/src/public/node/fs.test.ts relies heavily on mocking internal libraries like fast-glob and os, which leads to tests that assert on implementation details (e.g., "was this function called with these arguments") rather than actual behavior (e.g., "did the function find the correct files").

WHAT is this pull request doing?

• Removed top-level mocks for fast-glob, os, and array in packages/cli-kit/src/public/node/fs.test.ts.
• Refactored glob tests to create real files in a temporary directory and verify the results.
• Refactored generateRandomNameForSubdirectory tests to use vi.spyOn for targeted mocking of the reroll logic.
• Simplified detectEOL tests to use real os.EOL values.
• Cleaned up redundant vi.doMock calls.

How to test your changes?

CI

Checklist

• I've considered possible cross-platform impacts (Mac, Linux, Windows)
• I've considered possible documentation changes
• I've considered analytics changes to measure impact
• The change is user-facing — No (it's a test-only change)

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PR created automatically by Jules for task 4717222672129663433 started by @gonzaloriestra

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[byrichardpowell]

Approving with 1 comment. That way you don't need a second review.

Totally open to the idea the comment I left is not worth addressing.