Use scalarFunctionExprToProtoWithReturnType for levenshtein

Override convert() to use scalarFunctionExprToProtoWithReturnType
with IntegerType, so the native planner skips the DataFusion
registry lookup and does not conflict with DataFusion's built-in
2-arg levenshtein function when 3 args (threshold) are passed.

Also fix Spotless: remove unnecessary string interpolation prefix.

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

Author: yusinnmao

spark/src/main/scala/org/apache/comet/serde/strings.scala

@@ -22,7 +22,7 @@ package org.apache.comet.serde
 import java.util.Locale
 
 import org.apache.spark.sql.catalyst.expressions.{Attribute, Cast, Concat, ConcatWs, Expression, GetJsonObject, If, InitCap, IsNull, Left, Length, Levenshtein, Like, Literal, Lower, RegExpReplace, Right, RLike, StringLPad, StringRepeat, StringRPad, StringSplit, Substring, Upper}
-import org.apache.spark.sql.types.{BinaryType, DataTypes, LongType, StringType}
+import org.apache.spark.sql.types.{BinaryType, DataTypes, IntegerType, LongType, StringType}
 import org.apache.spark.unsafe.types.UTF8String
 
 import org.apache.comet.CometConf
@@ -84,7 +84,7 @@ object CometLength extends CometScalarFunction[Length]("length") {
   }
 }
 
-object CometLevenshtein extends CometScalarFunction[Levenshtein]("levenshtein") {
+object CometLevenshtein extends CometExpressionSerde[Levenshtein] {
 
   override def getUnsupportedReasons(): Seq[String] = Seq(
     "Non-default collation (non-UTF8_BINARY) is not supported")
@@ -96,6 +96,19 @@ object CometLevenshtein extends CometScalarFunction[Levenshtein]("levenshtein")
       case _ => Compatible()
     }
   }
+
+  override def convert(
+      expr: Levenshtein,
+      inputs: Seq[Attribute],
+      binding: Boolean): Option[Expr] = {
+    val childExprs = expr.children.map(exprToProtoInternal(_, inputs, binding))
+    val optExpr = scalarFunctionExprToProtoWithReturnType(
+      "levenshtein",
+      IntegerType,
+      false,
+      childExprs: _*)
+    optExprWithInfo(optExpr, expr, expr.children: _*)
+  }
 }
 
 object CometInitCap extends CometScalarFunction[InitCap]("initcap") {

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

@@ -493,7 +493,7 @@ class CometStringExpressionSuite extends CometTestBase {
       sql(s"CREATE TABLE $table(s1 STRING, s2 STRING) USING parquet")
       sql(
         s"INSERT INTO $table VALUES " +
-          s"('abc', 'adc'), (NULL, 'test'), ('hello', NULL), (NULL, NULL)")
+          "('abc', 'adc'), (NULL, 'test'), ('hello', NULL), (NULL, NULL)")
       checkSparkAnswerAndOperator(s"SELECT levenshtein(s1, s2) FROM $table")
     }
   }