Optimze imports in ImageResponseMetadata.

* Make the Long created field final.
* Delegate the default constructor to ImageResponseMetadata(:Long) passing System.currentTimeMillis().

Author: jxblum

spring-ai-core/src/main/java/org/springframework/ai/image/ImageResponseMetadata.java

@@ -16,9 +16,6 @@
 package org.springframework.ai.image;
 
 import org.springframework.ai.model.MutableResponseMetadata;
-import org.springframework.ai.model.ResponseMetadata;
-
-import java.util.HashMap;
 
 /**
  * Represents metadata associated with an image response. It provides additional
@@ -31,10 +28,10 @@
  */
 public class ImageResponseMetadata extends MutableResponseMetadata {
 
-	private Long created;
+	private final Long created;
 
 	public ImageResponseMetadata() {
-		this.created = System.currentTimeMillis();
+		this(System.currentTimeMillis());
 	}
 
 	public ImageResponseMetadata(Long created) {