Summary
Hotfix related to the process of downloads: Mark item as improted was no longer being called as it should
Testing
Added test coverage to shield from future regression on the topic
Notes
While I was at it, I took the opportunity to rename GetClientDownloadItemId into GetExternalId in an effort to enhance the semantics used around the downloads and related interfaces (GetClientDownloadItemId and GetDownloadClientId are very confusing and did not convey the fact that this was not an ID managed by Listenarr)
Automated Canary build