Consider using `StableValue` when available in Java

[sbordet]

Jetty version(s)
12+

Enhancement Description
StableValue is introduced in a new JEP, likely in Java 25 as a preview, see:

• https://openjdk.org/jeps/8312611
• https://www.youtube.com/watch?v=3fXHrK3yV9w

We could use StableValues is many, many places in Jetty, with important performance gains.

Perhaps it may be introduced in a multi-release jar.