feat: support concat for strings

Author: comphead

fuzz-testing/src/main/scala/org/apache/comet/fuzz/Meta.scala

@@ -137,7 +137,10 @@ object Meta {
             SparkBinaryType,
             SparkArrayType(
               SparkTypeOneOf(Seq(SparkStringType, SparkNumericType, SparkBinaryType))))))),
-    createFunctionWithInputTypes("concat", Seq(SparkStringType, SparkStringType)), // TODO: variadic
+    createFunctionWithInputTypes(
+      "concat",
+      Seq(SparkStringType, SparkStringType)
+    ), // TODO: variadic
     createFunctionWithInputTypes("concat_ws", Seq(SparkStringType, SparkStringType)),
     createFunctionWithInputTypes("contains", Seq(SparkStringType, SparkStringType)),
     createFunctionWithInputTypes("ends_with", Seq(SparkStringType, SparkStringType)),