[Tests] Add unit tests for ShopifyConfig custom oclif loader

[gonzaloriestra]

WHY are these changes introduced?

Enhance codebase coverage and reliability by fully testing the ShopifyConfig custom oclif loader class.

WHAT is this pull request doing?

This pull request introduces a comprehensive suite of unit tests for ShopifyConfig inside packages/cli-kit/src/public/node/custom-oclif-loader.test.ts covering:

• Delegation to super when no custom lazy loader is provided.
• Handling when commands are not found.
• Handing when the lazy command loader returns undefined.
• Handling when command classes are loaded and successfully run, including prerun/postrun hooks dispatching.
• Falling back to root plugins when command plugins are undefined.
• Proper usage of cached commands.

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 16676749889839662627 started by @gonzaloriestra

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