[Tests] Add unit tests for unionArrayStrategy

[gonzaloriestra]

WHY are these changes introduced?

Fixes #0000

Increases test coverage by adding unit tests for the untested unionArrayStrategy helper in packages/cli-kit/src/private/common/array.ts.

WHAT is this pull request doing?

Adds a unit test suite in packages/cli-kit/src/private/common/array.test.ts to test:

• Array concatenation and duplicate removal with preserved element order.
• Merging empty arrays with populated arrays.
• Merging arrays without overlapping elements.

How to test your changes?

CI

Post-release steps

N/A

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 3459851513828265748 started by @gonzaloriestra

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