- Updated SFTP upload functions to utilize a new `wait_for_sftp_upload_io` helper for improved error handling and cancellation support.
- Adjusted concurrency settings for small file transfers to optimize performance.
- Introduced a `wait_for_transfer_cancelled` function to monitor and handle transfer cancellation events.
- Refactored the `PendingRequest` structure to manage timeouts and clean up pending requests effectively.
- Improved error handling in the SFTP client to ensure proper cleanup of pending requests on failure.