Bug fixes & build cleanup

Few fixes that have been sitting in the queue:

• Version checker now actually picks the higher version instead of always rejecting duplicates
• canLoad is now thread-safe
• Dropped a dead branch in the version parser (the regex check was unreachable after the digit-only strip)
• Fixed the broken Java snippet in the README (missing paren)

Build:

• Gradle 7.4 → 8.10.2 (so it builds on JDK 17/21)
• Output still targets Java 8 bytecode — verified running on JRE 8, 11, 17, and 21
• CI now uses JDK 17 + Temurin via setup-java@v4
• Added a MIT license

Full Changelog: 3.0...4.0