With Java 21, should have support for virtual threads - with virtual threadpool support

[nmondal]

Because most of the cron operations are are doing is massively IO centric.
I will raise a PR soon to do the same.
Please let me know if this is going to be useful or not.
It can be done with - DirectSchedulerFactory anyways by switching the threadpool:

DirectSchedulerFactory.CreateScheduler Method (IThreadPool, IJobStore)

with RAMJobStore

[melloware]

@nmondal please submit the PR.

[nmondal]

Here is the PR.
#1093

Some tests fail while running in JDK-21, but I have ensured that the portion of the added code is tested fully and runs under any JRE.

[ravi-inflection]

@melloware Can you please look into the PR.