[Tests] Add unit tests for flushPromises utility

[gonzaloriestra]

WHY are these changes introduced?

The flushPromises utility in @shopify/cli-kit was identified as lacking dedicated unit tests. Adding these tests ensures the utility correctly handles various asynchronous scenarios, making the codebase safer to change.

WHAT is this pull request doing?

Introduces packages/cli-kit/src/public/node/promises.test.ts which tests:

• Simple microtasks completion.
• Chained/nested microtasks completion.
• Macrotasks scheduled via setImmediate.

How to test your changes?

CI

Post-release steps

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 10896329056256182399 started by @gonzaloriestra

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[gonzaloriestra]

Merge activity

• Jul 13, 1:55 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Jul 13, 1:55 PM UTC: @gonzaloriestra added this pull request to the GitHub merge queue with Graphite.