server: add auto-sleep after N seconds of idle (#18228)

* implement sleeping at queue level

* implement server-context suspend

* add test

* add docs

* optimization: add fast path

* make sure to free llama_init

* nits

* fix use-after-free

* allow /models to be accessed during sleeping, fix use-after-free

* don't allow accessing /models during sleep, it is not thread-safe

* fix data race on accessing props and model_meta

* small clean up

* trailing whitespace

* rm outdated comments

tools/cli/cli.cpp

@@ -209,8 +209,6 @@ int main(int argc, char ** argv) {
         return 1;
     }
 
-    ctx_cli.ctx_server.init();
-
     console::spinner::stop();
     console::log("\n");