/**
 * Parse a flexible timestamp string into milliseconds since epoch.
 *
 * Accepts:
 * - Unix milliseconds as a numeric string (e.g., "1700000000000")
 * - Relative time shorthand (e.g., "30s", "5m", "1h", "2d", "1w")
 * - ISO 8601 date or datetime string (e.g., "2023-01-01", "2023-01-01T00:00:00Z")
 */
export declare function parseTimestamp(input: string, label?: string): number;