[Tests] os username utility coverage

[gonzaloriestra]

WHY are these changes introduced?

Enhance unit test coverage for the username utility in os.ts. Previously, the module lacked comprehensive tests covering its multiple fallback layers, platform-specific code paths, and logical conditions.

WHAT is this pull request doing?

This pull request implements thorough unit tests for the username utility inside packages/cli-kit/src/public/node/os.test.ts.
Specifically, it covers:

• Early-return check for multiple priority environment variables (SUDO_USER, USER, C9_USER, LOGNAME, LNAME, USERNAME).
• Fallback check of calling os.userInfo() when priority environment variables are not set.
• Mocking and verifying the catch block for os.userInfo() when it throws an error.
• Checking platform-specific subprocess calls (Windows' whoami and Unix's id -u / id -un) when environment variables and userInfo are unavailable or throw errors.
• Verifying the fallback when POSIX name resolution fails (no-username-<uid>).
• All original platformAndArch tests are preserved.

How to test your changes?

CI

Post-release steps

None.

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 — I've identified the correct bump type (patch for bug fixes · minor for new features · major for breaking changes) and added a changeset with pnpm changeset add

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PR created automatically by Jules for task 10203123816950889352 started by @gonzaloriestra

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