refactor(JSONReader): Modify ResolveTask to final class

This change modifies the `ResolveTask` inner class in `JSONReader` to be `final`, enhancing the class's immutability and preventing subclassing.

core/src/main/java/com/alibaba/fastjson2/JSONReader.java

@@ -4498,7 +4498,7 @@ public abstract class JSONReader
         }
     }
 
-    static class ResolveTask {
+    static final class ResolveTask {
         final FieldReader fieldReader;
         final Object object;
         final Object name;