[PDGGK]

Follow-up to #18719, as discussed there.

Why

Since JDBC 4, DriverManager loads drivers through ServiceLoader from META-INF/services/java.sql.Driver, so an application can call DriverManager.getConnection("jdbc:iotdb://...") without first calling Class.forName. IoTDB's driver never took part in this. The file that existed before #18719 sat at services/META-INF/java.sql.Driver, with the directories in the wrong order, and its license header was a /* */ block, which provider files do not accept. Before #18719 a <resources> override in the jdbc pom also kept src/main/resources out of the jar. None of the released jars from 0.9.3 to 2.0.11 that I checked contain a provider file at either path, so every client has needed Class.forName("org.apache.iotdb.jdbc.IoTDBDriver").

Change

• Add iotdb-client/jdbc/src/main/resources/META-INF/services/java.sql.Driver naming org.apache.iotdb.jdbc.IoTDBDriver. The license header uses # comments, like the other provider files in the repo.
• Add DriverServiceRegistrationTest. It asks ServiceLoader for java.sql.Driver providers and expects an IoTDBDriver among them. Going through ServiceLoader rather than DriverManager keeps the test independent of other tests that already loaded the driver class, which registers it as a side effect. The test is in a new file because Improve JDBC driver metadata #17865 adds IoTDBDriverTest.java.

Class.forName keeps working, and the CLI, which uses it, is unaffected. The only behaviour change is that DriverManager now finds the driver on its own.

Testing

• The new test passes on a clean build. With the provider file removed, a clean build fails it with META-INF/services/java.sql.Driver should name IoTDBDriver. An incremental build hid that failure behind a stale copy in target/classes, so I checked this with clean.

• The jdbc module's 74 tests and the 47 tests in the modules it depends on pass. spotless:check passes.

• Against a running IoTDB 2.0.8, I ran a client that calls only DriverManager.getConnection("jdbc:iotdb://127.0.0.1:6667/", ...) and runs show version:

  classpath	without Class.forName	with Class.forName
  CLI lib/ built from this branch	connects, returns 2.0.8	connects
  iotdb-jdbc-*-jar-with-dependencies.jar from this branch	connects, returns 2.0.8	not run
  CLI lib/ built before this change	No suitable driver found	connects