Upgrade project from Java 17 to Java 21#203

Draft

Copilot wants to merge 2 commits intomainfrom

copilot/fix-40b4f568-ab0b-41c7-a10e-70e5dcdcbce5

Commits on Aug 24, 2025

Initial plan
Copilot
committed
Update all build files to use JDK 21

Copilot
and
75py
committed