/**
 * Return the number of days in the calendar year containing `value`.
 *
 * - 365 for a common year, 366 for a leap year.
 * - Returns null on invalid input.
 *
 * @param value ISO PlainDate string
 * @returns 365 or 366, or null on invalid input
 *
 * @example getDaysInYear("2024-06-15") // 366 (leap year)
 * @example getDaysInYear("2023-06-15") // 365
 * @example getDaysInYear("invalid") // null
 */
export declare function getDaysInYear(value: string): number | null;