server: add "schema" and validation (#24150)

* wip

* working

* correct some limits

* add field name to error message

tools/server/server-task.h

@@ -210,13 +210,6 @@ struct server_task {
         }
     }
 
-    static task_params params_from_json_cmpl(
-        const llama_vocab * vocab,
-        const common_params & params_base,
-        const int n_ctx_slot,
-        const std::vector<llama_logit_bias> & logit_bias_eog,
-        const json & data);
-
     // utility function
     static std::unordered_set<int> get_list_id(const std::vector<server_task> & tasks) {
         std::unordered_set<int> ids(tasks.size());