[java-storage] Improve Virtual Thread compatibility

With the release of Java 21 [Virtual Threads](https://docs.oracle.com/en/java/javase/21/core/virtual-threads.html) are now a first class feature.

To better support the use of virtual threads in applications we will need to evaluate and update certain assumptions and aspects the library is built upon today.

[Virtual Threads: An Adoption Guide](https://docs.oracle.com/en/java/javase/21/core/virtual-threads.html#GUID-B163BC51-039B-43BD-87ED-27BE384B509D) outlines several considerations we should keep in mind when doing this work.

Items to investigate:

0. [ ] Timeline for java 21 CI/CD infrastructure readiness
1. [x] `synchronized` method and blocks
2. [ ] Existing locking strategies
3. [ ] ExecutorService usage
4. [ ] Context propagation with other libraries (OTel, OpenCensus)
5. [ ] Parallel Stream usage
6. [ ] other `java.util.concurrent` usages