add support for Java 26

> Java 26 was officially released last month at JavaOne. You can rewatch the Java 26 launch and the JavaOne keynote here [1].

> With JDK 26 released, the focus now shifts to JDK 27 testing. At the time of writing, one JEP already targets JDK 27 (JEP 527: Post-Quantum Hybrid Key Exchange for TLS 1.3). To learn more about post-quantum cryptography, watch this JavaOne session [2] by Sean Mullan (OpenJDK Security Group Lead). I’ll conclude with a big shout-out to the Eclipse Collections team for already identifying a potential issue with JDK 27 early-access builds.

> [1] https://www.youtube.com/watch?v=3fLCOqpIfI0
> [2] https://www.youtube.com/watch?v=6xh-bN4W74o

The issue body contains release commentary but does not identify files, tests, entry points, or acceptance criteria. Start by clarifying what “support for Java 26” means for Spoon’s Java source parsing and transformation API, then locate the existing Java-version handling and tests. Done should include an explicit compatibility scope and passing coverage for Java 26 input.

Written by the indexing model from the issue text.