refactor: rename findRootCauseMessage to getCauseChainMessages

The method concatenates all messages in the cause chain, not just the
root cause. The new name accurately describes the behavior.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: dkropachev

integration-tests/src/test/java/com/datastax/oss/driver/core/clientroutes/ClientRoutesUnsupportedVersionIT.java

@@ -188,7 +188,7 @@ public void should_not_activate_on_unsupported_version() throws Exception {
                 + "with a clear error message");
       } catch (Exception e) {
         // The session init should fail with a message telling the user exactly what's wrong.
-        String message = findRootCauseMessage(e);
+        String message = getCauseChainMessages(e);
         assertThat(message)
             .as(
                 "Session init failure must mention CLIENT_ROUTES_CHANGE so the user knows "
@@ -203,8 +203,8 @@ public void should_not_activate_on_unsupported_version() throws Exception {
     }
   }
 
-  /** Walks the exception cause chain to find the root message. */
-  private static String findRootCauseMessage(Throwable t) {
+  /** Concatenates all messages in the exception cause chain. */
+  private static String getCauseChainMessages(Throwable t) {
     StringBuilder sb = new StringBuilder();
     while (t != null) {
       if (t.getMessage() != null) {