chore: Add @nowarn annotation to LazyVals.

[He-Pin]

Unsafe is planned to be removed in future Java versions.

Motivication:

Makes it compile on JDK 23
refs: https://openjdk.org/jeps/471

Modification:
Add @nowarn("cat=deprecation")

Result:
Compiles successfully on JDK 23

[som-snytt]

Non-core contributors may be more likely to keep their JDKs fresh.

[som-snytt]

Not sure if dotty has the "nowarn suppresses no warnings" lint, but it would be nice to ensure clean compilation across JDK versions.

Also not sure whether dotty exploits newer API or if releases are built under the --java-output-version-flag whatever that is called; or whether CI building under JDK 8 is relied upon.

[He-Pin]

Keep JEP 498: Warn upon Use of Memory-Access Methods in sun.misc.Unsafe
in mind too.

[som-snytt]

This remains a hassle. Maybe there is a big picture problem here, but I just want to switch back from JDK 17 after working on a dotty ticket. However, a glitch is that I can't buildQuick to test a ticket that relies on a magic scala_legacy version which seems to be just the old runner.

[Gedochao]

LGTM
As per https://www.scala-lang.org/news/next-scala-lts.html, we'll be migrating from the unsafe API soon. I think this is okay as a band-aid before Scala 3.8.

[SethTisue]

thank you @He-Pin !