/**
 * Return the end of the quarter for a given ISO datetime.
 *
 * - Returns the last moment of the quarter with time set to 23:59:59.999999999.
 * - Q1 ends on "03-31T23:59:59.999999999", Q2 ends on "06-30T23:59:59.999999999", etc.
 * - Validates input using isValidDateTime.
 *
 * @param value ISO PlainDateTime string
 * @returns ISO PlainDateTime string for the end of the quarter, or "" on invalid input
 *
 * @example endOfQuarterForDateTime("2024-03-15T12:00:00") // "2024-03-31T23:59:59.999999999"
 * @example endOfQuarterForDateTime("2024-06-15T12:00:00") // "2024-06-30T23:59:59.999999999"
 * @example endOfQuarterForDateTime("invalid") // ""
 */
export declare function endOfQuarterForDateTime(value: string): string;