Fix customs items bug

[nwithan8]

Description

• Fix bug where customs items were not being created if included in a customs info creation request

Testing

• New unit test to confirm function works as expected (E2E tested with and without patch to confirm)
• New cassettes for unit test

Pull Request Type

Please select the option(s) that are relevant to this PR.

• [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 not work as expected)
• [ ] Improvement (fixing a typo, updating readme, renaming a variable name, etc)

[nwithan8]

Walked through the library, comparing everything to the API docs to fix everywhere where data should be wrapped.

Called out a few places in the code where the data does not need to be wrapped, but is incorrect on the API docs (see TODOs)

Webhook is seeing some degraded performance. The create call is showing success, but the webhook is not appearing on the UI dashboard, and when attempting to then delete the webhook, we get a "Resource not found" error. As a result, the CI will fail until the issue is rectified