FIX ISSUE:The parameter max_tokens specified in the request are not valid: max_tokens and max_completion_tokens cannot be set at the same time;Refactor maxTokens assignment in AbstractLlmService (#177)

在依赖的agentscope中OpenAIChatFormatter.java第107-110行，代码同时将maxTokens设置到了OpenAIRequest的maxCompletionTokens和maxTokens两个字段中，这导致了API返回400错误，因为这两个参数是互斥的。根据OpenAI API文档，max_completion_tokens是较新的参数，用于替代max_tokens，所以应该只设置其中一个。

Co-authored-by: daofeng <xujingfeng95@gmail.com>

Author: darkwu

himarket-server/src/main/java/com/alibaba/himarket/service/hichat/service/AbstractLlmService.java

@@ -176,7 +176,7 @@ protected ModelFeature getOrDefaultModelFeature(ProductResult product) {
 
         return ModelFeature.builder()
                 .model(modelFeature.getModel())
-                .maxTokens(ObjectUtil.defaultIfNull(modelFeature.getMaxTokens(), 5000))
+                .maxTokens(modelFeature.getMaxTokens())
                 .temperature(ObjectUtil.defaultIfNull(modelFeature.getTemperature(), 0.9))
                 .streaming(ObjectUtil.defaultIfNull(modelFeature.getStreaming(), true))
                 .webSearch(ObjectUtil.defaultIfNull(modelFeature.getWebSearch(), false))