/**
 * Return the current microsecond from 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 microsecond string (zero-padded to 3 digits) or "" on failure
 *
 * @example getUtcMicrosecond() // "456"
 * @example getUtcMicrosecond() // "" (on failure)
 */
export declare function getUtcMicrosecond(): string;