feat(dnssec): Add MX record DNSSEC support for proper serialization and authentication of mail exchange records

ts_server/classes.dnsserver.ts

@@ -809,6 +809,12 @@ export class DnsServer {
         minimum.writeUInt32BE(data.minimum, 0);
         
         return Buffer.concat([mname, rname, serial, refresh, retry, expire, minimum]);
+      case 'MX':
+        // MX records contain preference (16-bit) and exchange (domain name)
+        const preference = Buffer.alloc(2);
+        preference.writeUInt16BE(data.preference, 0);
+        const exchange = this.nameToBuffer(data.exchange);
+        return Buffer.concat([preference, exchange]);
       // Add cases for other record types as needed
       default:
         throw new Error(`Serialization for record type ${type} is not implemented.`);