fix: clear explain info tags before fallback in auto scan mode

When nativeDataFusionScan fails and adds explain info tags to the
scanExec node, those tags leak into the nativeIcebergCompatScan
fallback path. Clear tags with unsetTagValue before attempting the
fallback to prevent contamination.

Author: andygrove

spark/src/main/scala/org/apache/comet/rules/CometScanRule.scala

@@ -41,7 +41,7 @@ import org.apache.spark.sql.execution.datasources.v2.csv.CSVScan
 import org.apache.spark.sql.internal.SQLConf
 import org.apache.spark.sql.types._
 
-import org.apache.comet.{CometConf, CometNativeException, DataTypeSupport}
+import org.apache.comet.{CometConf, CometExplainInfo, CometNativeException, DataTypeSupport}
 import org.apache.comet.CometConf._
 import org.apache.comet.CometSparkSessionExtensions.{isCometLoaded, withInfo, withInfos}
 import org.apache.comet.DataTypeSupport.isComplexType
@@ -169,7 +169,12 @@ case class CometScanRule(session: SparkSession)
         COMET_NATIVE_SCAN_IMPL.get() match {
           case SCAN_AUTO =>
             nativeDataFusionScan(plan, session, scanExec, r, hadoopConf)
-              .orElse(nativeIcebergCompatScan(session, scanExec, r, hadoopConf))
+              .orElse {
+                // Clear explain info tags from the failed nativeDataFusionScan
+                // attempt so they don't leak into the fallback path
+                scanExec.unsetTagValue(CometExplainInfo.EXTENSION_INFO)
+                nativeIcebergCompatScan(session, scanExec, r, hadoopConf)
+              }
               .getOrElse(scanExec)
           case SCAN_NATIVE_DATAFUSION =>
             nativeDataFusionScan(plan, session, scanExec, r, hadoopConf).getOrElse(scanExec)