Do ephemeral deletion in async task background loop (#3194)

* Do ephemeral deletion in background loop

1. in start_io start ephemeral async task, in stop_io cancel ephemeral async task

2. start ephemeral async task which loops like this:

- wait until next time a message deletion is needed or an interrupt occurs (see 3.)
- perform delete_expired_messages including sending MSGS_CHANGED events

3. on new messages (incoming or outgoing) with ephemeral timer:

- interrupt ephemeral async task

* Changelog

* Fix and improve test

* no return value needed

* address @link2xt review comments

* slight normalization: have only one place where we wait for interrupt_receiver

* simplify sql statement -- and don't exit the ephemeral_task if there is an sql problem but rather wait

* Remove now-unused `ephemeral_task` JoinHandle

The JoinHandle is now inside the Scheduler.

* fix clippy

* Revert accidental move of the line

* Add log

Co-authored-by: holger krekel <holger@merlinux.eu>
Co-authored-by: link2xt <link2xt@testrun.org>

src/context.rs

@@ -10,7 +10,6 @@ use async_std::{
     channel::{self, Receiver, Sender},
     path::{Path, PathBuf},
     sync::{Arc, Mutex, RwLock},
-    task,
 };
 
 use crate::chat::{get_chat_cnt, ChatId};
@@ -56,7 +55,6 @@ pub struct InnerContext {
     pub(crate) events: Events,
 
     pub(crate) scheduler: RwLock<Scheduler>,
-    pub(crate) ephemeral_task: RwLock<Option<task::JoinHandle<()>>>,
 
     /// Recently loaded quota information, if any.
     /// Set to `None` if quota was never tried to load.
@@ -176,7 +174,6 @@ impl Context {
             translated_stockstrings: RwLock::new(HashMap::new()),
             events: Events::default(),
             scheduler: RwLock::new(Scheduler::Stopped),
-            ephemeral_task: RwLock::new(None),
             quota: RwLock::new(None),
             creation_time: std::time::SystemTime::now(),
             last_full_folder_scan: Mutex::new(None),
@@ -642,10 +639,6 @@ impl InnerContext {
                 lock.stop(token).await;
             }
         }
-
-        if let Some(ephemeral_task) = self.ephemeral_task.write().await.take() {
-            ephemeral_task.cancel().await;
-        }
     }
 }