/**
 * Return the current microsecond using the system timeZone.
 *
 * - Uses Temporal.Now.plainDateTimeISO to get current microsecond in system timezone.
 * - Returns zero-padded string to 3 digits (e.g., "456").
 * - Returns "" when system timezone is unavailable.
 *
 * @returns current microsecond string (zero-padded to 3 digits) or "" on invalid
 *
 * @example getMicrosecond() // "000"
 * @example getMicrosecond() // "" (when system timeZone unavailable)
 */
export declare function getMicrosecond(): string;