Add support for virtual threads

[bdeneuter]

Hi,

This is a feature request.
Virtual threads were added to the JDK in JDK 21. It still had an issue with pinning which has been fixed with https://openjdk.org/jeps/491 in JDK 24.
JDK 25 became the first LTS which has support for virtual threads without the pinning issue.
It would be nice to have support for virtual threads for processing when running on JDK 25.
I created a fork with a first implementation but I didn't find the time to get the Maven build working correctly.
I tried to keep the original build and have only the module parallel-consumer-virtual-threads build on JDK 25 but didn't succeed yet.
You find a rough version from the code here:
https://github.com/bdeneuter/parallel-consumer/blob/master/parallel-consumer-virtual-threads/src/main/java/io/confluent/parallelconsumer/virtual_thread/VirtualThreadProcessor.java

I based the implementation on the reactor version.