* fix: refactoring
* chore: add google-cloud-storage and google-cloud-auth deps
* feat: add GCS provider config model
* feat: add GCS credential, client, and stream-source helpers
StreamSource bridges build_stream's Send-only byte stream into the SDK's
StreamingSource (which send_buffered requires to be Send+Sync+'static) via a
bounded mpsc channel, avoiding any change to the shared UploadStream type.
* feat: implement GCS StorageProvider upload
* feat: register google-cloud-storage provider in factory
* test: GCS upload roundtrip against fake-gcs-server
* fix: format GCS bucket as projects/_/buckets/<name> in upload_with_client
write_object rejects the bare bucket id with "malformed bucket name"; the
production provider passed config.bucket_name unformatted, so real uploads
would always fail. Format once in upload_with_client so prod and the
fake-gcs-server test share the corrected path.
* style: cargo fmt GCS provider files
* fix: gcs
Charles GTE