Update bundled JRE to Java 25

[amritamishra01]

Summary

Updates the bundled JustJ runtime from Java 21 to Java 25.

Changes

• Updated default bundled JRE version in scripts/jre.mjs
• Updated release workflow packaging step to download Java 25 runtime
• Updated CLI usage example in scripts/index.mjs

Validation

• Verified LATEST_JRE now points to 25
• Verified release workflow packages VSIX with --javaVersion 25
• Verified CLI usage example reflects Java 25

Fixes #4353

[wenytang-ms]

I gave this a spin on a real JDK 25 (Temurin 25.0.3) — launched the bundled server and imported actual projects over LSP. Mostly looks great, but I hit one thing worth calling out before release.

Stuff that works fine on 25:

• Server boots and the LSP handshake is clean, no class-version/OSGi errors.
• Maven imports/builds with 0 errors, both ECJ and javac.enabled. All the jdk.compiler/* add-opens are still valid on 25.
• Lombok 1.18.39 agent loads fine and generates accessors correctly.

The catch — Gradle:
Opening a Gradle 8.5 project blows up with Unsupported class file major version 69 → "Can't use Java 25.0.3 and Gradle 8.5". The embedded JRE is what Buildship uses to run Gradle unless you set java.import.gradle.java.home, so this hits the default setup. Gradle''s matrix says running on JDK 25 needs Gradle >= 9.1.0, whereas 21 was happy with 8.5 — so this bumps the floor a lot and breaks most Gradle 8.x projects. Basically the same thing as #4018.

So: totally fine to merge, the runtime''s ready on 25. But two things would be nice — a heads-up in the release notes that Gradle < 9.1.0 folks need to upgrade Gradle or point java.import.gradle.java.home at a JDK <= 21, and maybe sort out the "Java 25" wording from #4182 while we''re at it.