refactor: consolidate HoptimatorDdlExecutor tests into single test class

Merged HoptimatorDdlExecutorDdlTest and HoptimatorDdlExecutorMockServiceTest
into HoptimatorDdlExecutorTest, removing duplicate helpers and the redundant
testDdlExecutorWithWritableConnection assertion.

Author: jogrogan

hoptimator-jdbc/src/main/java/com/linkedin/hoptimator/jdbc/HoptimatorDdlUtils.java

@@ -608,7 +608,7 @@ public static List<String> specifyFromSql(String sql, HoptimatorConnection conn)
     }
 
     if (sqlNode.getKind().belongsTo(SqlKind.DDL)) {
-      throw new SQLException("Unsupported DDL statement for !specify: " + sql);
+      throw new SQLException("Unsupported DDL statement: " + sql);
     }
 
     // Plain SELECT / INSERT INTO path.