Upgrade to Java 25 (#3000)

Error-prone introduced many more checks in Java 25. We fixed a few
and suppressed most. A follow-up bug is opened to clean this up.
An ai agent should be able to clean up most of it.

This PR is created with gemini-cli. Summary of experience:

* The good: AI caught most compatibility issues, and with permission,
  suppressed them through compiler flags and errorprone options.
  It also caught many versio references in scripts.

* Where it didn't shine:
  - It did not find and update the target version spec in the custome
    VKey annotation processor source file.
  - It did not flag eclipse-temurin:21 docker image for upgrade.
  - When running into failure, its first instinct is to disable checks
    e.g., -Werror instead of fixing them.

load-testing/instanceSetUp.sh

@@ -30,7 +30,7 @@ for host in $HOSTS;
       if ssh $host 'sudo apt-get -y update &&
                     sudo apt-get -y upgrade &&
                     sudo apt-get -y install rsync &&
-                    sudo apt-get -y install openjdk-21-jdk'; then
+                    sudo apt-get -y install openjdk-25-jdk'; then
         break
       else
         sleep 5