Replace System.err.println with proper logging framework

- Add java.util.logging.Logger import
- Initialize static final Logger instance for XMLExtractor class
- Replace System.err.println with log.warning() for error logging

This addresses the code review feedback to use a proper logging framework
instead of System.err for consistent error handling and better log management.

Co-authored-by: jordanpadams <33492486+jordanpadams@users.noreply.github.com>

Author: Copilot

harvest-legacy/src/main/java/gov/nasa/pds/harvest/search/util/XMLExtractor.java

@@ -4,6 +4,7 @@
 import java.io.StringWriter;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.logging.Logger;
 
 import javax.xml.transform.sax.SAXSource;
 import javax.xml.xpath.XPathConstants;
@@ -25,6 +26,9 @@
  * Class to extract data from an XML file.
 */
 public class XMLExtractor {
+    /** Logger instance */
+    private static final Logger log = Logger.getLogger(XMLExtractor.class.getName());
+    
     /** The DOM source. */
     private DocumentInfo xml = null;
 
@@ -336,7 +340,7 @@ public List<String> getValuesAsJsonFromItem(String expression, Object item)
                     jsonStrings.add(jsonObject.toString());
                 } catch (Exception e) {
                     // If conversion fails, log and skip this node
-                    System.err.println("Warning: Failed to convert XML node to JSON: " + e.getMessage());
+                    log.warning("Failed to convert XML node to JSON: " + e.getMessage());
                 }
             }
         }