Closes #3922

What and why?

These modules have been used historically to handle issues with sun.misc.Unsafe/ lazy val implementations in Scala 3.0-3.2.
This is AFAIK no longer needed in modern Scala versions.
As pre-3.3 Scala is no longer supported, I am dropping those from the repository.
We still keep the dependency on old versions of those modules for the time being, just so that one could build native images with Scala 3.0-3.2, although that code path is deprecated for future removal.

Changes

• when generating a native image on Graal with Scala 3.0-3.2, the user will now get a warning

  [warning] building native images with Scala 3 older than 3.3.0 is deprecated.
  [warning] support will be dropped in a future Scala CLI version.
  [warning] it is advised to upgrade to a more recent Scala version
  

• removed 3 modules from the project, their usage is frozen at the last published version (1.9.1)
  • scala3-runtime
  • scala3-graal
  • scala3-graal-processor

Potential follow-ups

Were we to ever bump the internal JDK to 24 or higher, we'd need to remove this completely; for now, seems rather harmless to leave this as status quo.
We can consider removing it when we bump internal Scala to 3.9 - as far as I see it, Scala 3.0-3.2 is EOL, anyways. So perhaps sometime in 2026.

Further reading

• Graal scala3 #830
• Support Scala3 Graalvm bytecode manipulation for native-image alexarchambault/mill-native-image#20
• Native image binary doesn't run using plugin. Works with scala-cli. alexarchambault/mill-native-image#19
• New lazy vals implementation scala/scala3#15296
• Stabilize new lazy vals scala/scala3#16614