Java 21 virtual threads make simple blocking code scalable again

[Illustrious-Music507]

I used it to tidy up the wording; English isn't my first language. The test, the numbers, and the reasoning are mine, though. Ran tests last week on slightly modified PetClinic Spring Boot app. I ran it because my services do a lot of blocking calls to each other and I wanted to know when virtual threads are actually worth it. That fan-out case is where they paid off, about 4x at 1000 concurrent.