v5.0.0

Changes

• Harden provider configuration for long-lived workers.
• Fail fast on conflicting provider environment collisions.
• Reject provider names that normalize to an empty rclone remote name.
• Add instance-scoped flags, envs, and timeouts.
• Generate unique temporary local provider names for upload/download helpers.
• Create automatic download temp directories with owner-only permissions.
• Add SFTP private_key/key_pem support and reject ambiguous key_pem + key_file configs.
• Include configuration/security tests in the fast test path.