Revert to OAI-compatible args (ggml-org#20213)

* Revert to OAI-compatible args

* Apply workaround::func_args_not_string

Author: pwilkin

common/chat.cpp

@@ -129,7 +129,7 @@ json common_chat_msg::to_json_oaicompat(bool concat_typed_text) const {
                 {"type", "function"},
                 {"function", {
                     {"name", tool_call.name},
-                    {"arguments", json::parse(tool_call.arguments)},
+                    {"arguments", json(tool_call.arguments)},
                 }},
             };
             if (!tool_call.id.empty()) {
@@ -1353,6 +1353,8 @@ static common_chat_params common_chat_templates_apply_jinja(const struct common_
     params.add_bos = tmpls->add_bos;
     params.add_eos = tmpls->add_eos;
 
+    workaround::func_args_not_string(params.messages);
+
     if (!tmpl.original_caps().supports_system_role) {
         workaround::system_message_not_supported(params.messages);
     }

tests/test-chat.cpp

@@ -1434,9 +1434,7 @@ static void test_msgs_oaicompat_json_conversion() {
                               "        \"type\": \"function\",\n"
                               "        \"function\": {\n"
                               "          \"name\": \"python\",\n"
-                              "          \"arguments\": {\n"
-                              "            \"code\": \"print('hey')\"\n"
-                              "          }\n"
+                              "          \"arguments\": \"{\\\"code\\\":\\\"print('hey')\\\"}\"\n"
                               "        }\n"
                               "      }\n"
                               "    ]\n"