2.0.0 JAVA 21

• Adapted to JAVA 21 virtual threads.
• Changed the interface to be less noisy. (not compatible with previous versions)

        <dependency>
            <groupId>io.github.paxel</groupId>
            <artifactId>lintstone-actor-system</artifactId>
            <version>2.0.0</version>
        </dependency>