Mail sending optimization - implemented mail queue. Some minor optimizations.

src/main.rs

@@ -3,7 +3,7 @@ use leptos_captcha::spow::pow::Pow;
 use log::error;
 use rezervator::backend::appearance::check_appearance;
 use rezervator::backend::company::check_company;
-use rezervator::backend::mail::check_messages;
+use rezervator::backend::mail::{check_messages, Mailer};
 use rezervator::backend::user::create_admin;
 
 #[cfg(feature = "ssr")]
@@ -58,7 +58,8 @@ async fn main() -> std::io::Result<()> {
         .connect(&srv_conf.database().con_string()).await.unwrap();
     migrate!().run(&pool).await.expect("could not run SQLx migrations");
 
-    let mailing = srv_conf.mailing().clone();
+    let mut mailer = Mailer::new(srv_conf.mailing());
+    mailer.start_sender();
 
     if let Err(e) = create_admin(&pool).await {
         error!("Error while checking admin user: {:?}", e);
@@ -78,7 +79,7 @@ async fn main() -> std::io::Result<()> {
         let site_root = &leptos_options.site_root;
 
         App::new()
-            .app_data(Data::new(AppData::new(pool.clone(), mailing.clone())))
+            .app_data(Data::new(AppData::new(pool.clone(), mailer.clone())))
             .wrap(Logger::default())
             .wrap(Authentication)
             .wrap(SessionMiddleware::new(