test: Add additional contains expression tests

Add test coverage for null haystack, case sensitivity, and
both-columns (array-array) path for the optimized contains
implementation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: andygrove

spark/src/test/scala/org/apache/comet/CometExpressionSuite.scala

@@ -1181,6 +1181,21 @@ class CometExpressionSuite extends CometTestBase with AdaptiveSparkPlanHelper {
       // Test with pattern at end
       val queryEnd = sql(s"select id from $table where contains (name, 'Smith')")
       checkSparkAnswerAndOperator(queryEnd)
+
+      // Test with null haystack
+      sql(s"insert into $table values(6, null)")
+      checkSparkAnswerAndOperator(sql(s"select id, contains(name, 'Rose') from $table"))
+
+      // Test case sensitivity (should not match)
+      checkSparkAnswerAndOperator(sql(s"select id from $table where contains(name, 'james')"))
+    }
+  }
+
+  test("contains with both columns") {
+    withParquetTable(
+      Seq(("hello world", "world"), ("foo bar", "baz"), ("abc", ""), (null, "x"), ("test", null)),
+      "tbl") {
+      checkSparkAnswerAndOperator(sql("select contains(_1, _2) from tbl"))
     }
   }