support FileContent deserialization (#46)

Co-authored-by: flycloud_hz <flycloud_hz@gmail.com>

Author: flycloud-hz

a2a4j-core/src/main/java/io/github/a2ap/core/model/FileContent.java

@@ -18,13 +18,23 @@
 
 import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.annotation.JsonProperty;
+import com.fasterxml.jackson.annotation.JsonSubTypes;
+import com.fasterxml.jackson.annotation.JsonTypeInfo;
 
 import java.util.Objects;
 
 /**
  * Represents the content of a file.
  */
 @JsonInclude(JsonInclude.Include.NON_NULL)
+@JsonTypeInfo(
+        use = JsonTypeInfo.Id.DEDUCTION,
+        defaultImpl = FileContent.class
+)
+@JsonSubTypes({
+        @JsonSubTypes.Type(FileWithBytes.class),
+        @JsonSubTypes.Type(FileWithUri.class)
+})
 public abstract class FileContent {
 
     /**