Update contrib/langchain4j/src/main/java/com/google/adk/models/langchain4j/LangChain4j.java

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: curefat

contrib/langchain4j/src/main/java/com/google/adk/models/langchain4j/LangChain4j.java

@@ -436,9 +436,7 @@ private List<ToolSpecification> toToolSpecifications(LlmRequest llmRequest) {
                     if (jsonSchemaObj instanceof Schema) {
                       schema = (Schema) jsonSchemaObj;
                     } else {
-                      ObjectMapper adkMapper = JsonBaseModel.getMapper();
-                      String jsonSchemaStr = adkMapper.writeValueAsString(jsonSchemaObj);
-                      schema = adkMapper.readValue(jsonSchemaStr, Schema.class);
+                      schema = JsonBaseModel.getMapper().convertValue(jsonSchemaObj, Schema.class);
                     }
                   } catch (Exception e) {
                     throw new IllegalStateException(