Update Javadoc to reflect use of record vs lobok @value

Author: codesungrape

src/main/java/com/codesungrape/hmcts/bookapi/dto/BookRequest.java

@@ -4,10 +4,16 @@
 import jakarta.validation.constraints.NotBlank;
 
 /**
- * DTO representing the required input for creating or replacing a Book resource. This class mirrors
- * the OpenAPI 'BookInput' schema. @Value: Makes fields final, adds constructor, getters, equals,
- * hashCode, toString. @NotBlank: Field required; empty/missing value returns 400 Bad Request in
- * Spring. @JsonProperty: Maps snake_case JSON to camelCase Java using Jackson.
+ * DTO representing the required input for creating or replacing a Book resource.
+ * This record mirrors the OpenAPI 'BookInput' schema.
+ *As a Java record:
+ * - all fields are implicitly final
+ * - a canonical constructor is generated automatically
+ * - accessor methods (e.g., title()) are generated
+ * - equals, hashCode, and toString are automatically implemented
+ *`@NotBlank` ensures that each field is required; missing or empty values result in
+ * a 400 Bad Request response in Spring.
+ * `@JsonProperty` maps snake_case JSON to camelCase Java properties using Jackson.
  */
 public record BookRequest(
     @JsonProperty("title") @NotBlank(message = "Title is required") String title,