Implement OpenAI's response API and add support for built-in tools (web search & code interpreter).

src/agent/provider/openai_compat/config.rs

@@ -95,6 +95,7 @@ impl TryInto<OpenAITextGenerationConfig> for TextGenerationConfig {
             max_response_tokens: self.max_response_tokens,
             max_completion_tokens: None,
             max_context_tokens: self.max_context_tokens,
+            tools: Default::default(),
         })
     }
 }