Upgraded Java compile and runtime target from 8 to 21 (LTS).
Replaced / with in maven-compiler-plugin for stricter cross-compilation.
Updated maven-compiler-plugin from 3.2 to 3.13.0.
Updated Dockerfile base image from openjdk:8u332-slim-bullseye to eclipse-temurin:21-jre.
Updated CI build matrix from [8, 11, 17] to [17, 21]; Docker image now built and pushed on JDK 21.
Added validator-build/scripts/rotate-keystore.sh for rotating the self-signed ASiC-E signing certificate.
Rotated expired self-signed keystore (keystore-self-signed.jks); fixes Unable to verify signature during make validator in rule repos such as eforms-sdk-nor.
Extended Makefile with help, test, rotate_keystore, docker_run and version targets; removed obsolete DOCKER_CLI_EXPERIMENTAL flag.
Updated Lombok 1.18.28 → 1.18.36 (Java 21 compatibility – JCTree$JCImport.qualid removed in Java 21).
Updated JaCoCo 0.8.8 → 0.8.12 (Java 21 compatibility – class file major version 65 support).
Updated dependencies.
Full Changelog: 2.3.0...v2.4.0