v0.1.1 of tus_background_upload

TUS resumable uploads that keep running while the app is backgrounded or the device is locked, over native transports (iOS background URLSession, Android WorkManager via background_downloader). Changelog excerpt: - **Fix:**the TUS PATCH was sent with the file's own mime type (e.g. video/mp4) instead of application/offset+octet-stream, so spec-compliant servers (Bunny among them) rejected it. background_downloader's native binary-upload code overwrites the Content-Typeheader with the task's mimeTypeon both platforms; the transport now sets mimeTypeto the TUS content type explicitly. - A failed PATCH now folds the HTTP response code, exception description, and response body into the thrown `Htt[...]