/// TLS mode for PostgreSQL connections.
///
/// `Disable` uses plaintext connections (`tokio_postgres::NoTls`) — the
/// pre-v1.4 default, kept for backward compatibility.
///
/// `Require` enforces TLS via the platform's native TLS implementation
/// (SChannel on Windows, OpenSSL on Linux, Secure Transport on macOS). The
/// connector is cloned per pool acquisition, so it must be `Clone`
/// (`native_tls::TlsConnector` satisfies this).