avoid unnecessary copy

Co-authored-by: Georgi Gerganov <ggerganov@gmail.com>

Author: matteoserva

tools/server/utils.hpp

@@ -584,7 +584,7 @@ static json oaicompat_completion_params_parse(
     const json & body, /* openai api json semantics */
     bool use_jinja,
     common_reasoning_format reasoning_format,
-    const std::map<std::string,std::string> default_template_kwargs,
+    const std::map<std::string, std::string> & default_template_kwargs,
     const struct common_chat_templates * tmpls,
     bool allow_non_text,
     std::vector<raw_buffer> & out_files)