/**
 * Return the current nanosecond using the system timeZone.
 *
 * - Uses Temporal.Now.plainDateTimeISO to get current nanosecond in system timezone.
 * - Returns zero-padded string to 3 digits (e.g., "789").
 * - Returns "" when system timezone is unavailable.
 *
 * @returns current nanosecond string (zero-padded to 3 digits) or "" on invalid
 *
 * @example getNanosecond() // "000"
 * @example getNanosecond() // "" (when system timeZone unavailable)
 */
export declare function getNanosecond(): string;