Tests:
- [Both overloads] uses the `download.Link` to guess the filenamem if it's not present
- [Both overloads] returns null if `download.Link` is null
- [Both overloads] returns nuyll if `download.RdName` is null
- [Both overloads] works for a file in a deeply nested subdirectory
- [overload with `downloadPath` argument only] creates the correct directory
Tests:
- Downloads successfully when everything goes right first time
- Downloads successfully when the 5th api call is successful after 4 failures
- Fails to download when 5 api calls fail in a row
- Fails to download if the file has already been added to `Download Station` (when `GetInfoAsync` does not error)
- FAils to download if `remotePath` cannot be parsed by `Path.GetDirectoryName()`
