feat: delete messages on IMAP when deleting chat (#6613)

this PR deletes all known messages belonging to a chat when the chat is
deleted.

this may not be an exhaustive list as a client might not know all
message-ids (eg. when using different times for "delete from device").
in this case, other devices may know more IDs. otherwise, the chatmail
server will eventually clean up at some point. for non-chatmail, this is
up to the user then.

the deletion sql commands were inspired by
[`delete_msgs_ex`](https://github.com/chatmail/core/blob/main/src/message.rs#L1743)
(in fact, [a first
try](https://github.com/chatmail/core/compare/r10s/clear-chat-on-delete)
was adapting that part, however, that seems less performant as lots of
sql commands are needed)

successor of #5007

src/chat.rs

@@ -784,6 +784,7 @@ impl ChatId {
         );
 
         let chat = Chat::load_from_db(context, self).await?;
+        let delete_msgs_target = context.get_delete_msgs_target().await?;
         let sync_id = match sync {
             Nosync => None,
             Sync => chat.get_sync_id(context).await?,
@@ -792,6 +793,14 @@ impl ChatId {
         context
             .sql
             .transaction(|transaction| {
+                transaction.execute(
+                    "UPDATE imap SET target=? WHERE rfc724_mid IN (SELECT rfc724_mid FROM msgs WHERE chat_id=?)",
+                    (delete_msgs_target, self,),
+                )?;
+                transaction.execute(
+                    "DELETE FROM smtp WHERE msg_id IN (SELECT id FROM msgs WHERE chat_id=?)",
+                    (self,),
+                )?;
                 transaction.execute(
                     "DELETE FROM msgs_mdns WHERE msg_id IN (SELECT id FROM msgs WHERE chat_id=?)",
                     (self,),