fix: Async issues with handleHttpCallbackUnverified

[AmineI]

Hello,

Issues arise with testing SmartApp locally, due to handleHttpCallbackUnverified not being an async method.

As with other methods, and following the documentation, handleHttpCallbackUnverified now returns a Promise and can be properly awaited.

Types of changes

• [X] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [X] I have read the CONTRIBUTING document
• [X] My code follows the code style of this project (hint: install an xo editor plugin)
• [ ] Any required documentation has been added
• [ ] I have added tests to cover my changes

[AmineI]

Amended commit name to fix the commit-lint failed step 🙂.

[AmineI]

These changes were included as part of #259 . Thanks & well done ! I'll close this PR - A comment or heads-up here would have been appreciated, however :).

Have a great week-end !