FTP and SFTP steps add timeouts, retries, and reusable downloads

FTP and SFTP workflow steps now handle common file operations with better timeout, retry, and cleanup behavior.

• Download file content in a format that can be passed to later workflow steps.

• Retry uploads after temporary failures.

• Time out list, upload, download, rename, and close operations instead of hanging indefinitely.

• Report file operation errors more consistently.