/**
 * Return the current millisecond from the Unix timestamp in UTC as a zero-padded string.
 *
 * - Uses Temporal.Now.instant() converted to UTC zoned date time.
 * - Returns zero-padded string to 3 digits.
 * - Returns "" on failure.
 *
 * @returns current millisecond string (zero-padded to 3 digits) or "" on failure
 *
 * @example getUnixMillisecond() // "123"
 * @example getUnixMillisecond() // "" (on failure)
 */
export declare function getUnixMillisecond(): string;