Correct Nullable annotation package

Signed-off-by: Tran Ngoc Nhan <[email protected]>

Author: ngocnhan-tran1996

spring-ai-model/src/main/java/org/springframework/ai/model/AbstractResponseMetadata.java

@@ -22,7 +22,7 @@
 import java.util.concurrent.ConcurrentHashMap;
 
 import org.springframework.lang.NonNull;
-import io.micrometer.common.lang.Nullable;
+import org.springframework.lang.Nullable;
 
 public class AbstractResponseMetadata {
 

spring-ai-model/src/main/java/org/springframework/ai/model/MutableResponseMetadata.java

@@ -23,7 +23,7 @@
 import java.util.function.Function;
 
 import org.springframework.lang.NonNull;
-import io.micrometer.common.lang.Nullable;
+import org.springframework.lang.Nullable;
 
 public class MutableResponseMetadata implements ResponseMetadata {
 

spring-ai-model/src/main/java/org/springframework/ai/model/ResponseMetadata.java

@@ -21,7 +21,7 @@
 import java.util.function.Supplier;
 
 import org.springframework.lang.NonNull;
-import io.micrometer.common.lang.Nullable;
+import org.springframework.lang.Nullable;
 
 /**
  * Interface representing metadata associated with an AI model's response.