fix: Correctly delete unneeded messages on the server; Remove "Delete Messages from Server" (delete_server_after) config option (#8240)

Fix https://github.com/chatmail/core/issues/8195
Supersedes https://github.com/chatmail/core/pull/8217

The most interesting change is in `delete_expired_imap_messages()`
because there, messages are marked for deletion on single-device
chatmail profiles.

The logic in `delete_expired_imap_messages()` was wrong before, and
pre-messages were not deleted at all. This is fixed by also querying
`pre_rfc724_mid` in addition to `rfc724_mid` from the `msgs` table.
In order not to make the SQL statement too complex, I split it into two.

WRT tests:
- `test_immediate_autodelete()` tests the auto-deletion;
`test_imap_autodelete_fully_downloaded_msg()` tests that even for a
message that is split into pre- and post-message, both messages are
deleted.
- A lot of tests test that if bcc_self is on, messages are not
auto-deleted. E.g. `test_one_account_send_bcc_setting()` and
`test_markseen_message_and_mdn()` relies on the fact that messages stay
on the server when bcc_self is on.
- Unfortunately, it is not possible to test that messages are only
deleted for chatmail servers, because we don't have any tests that use a
non-chatmail server.

src/config.rs

@@ -194,17 +194,6 @@ pub enum Config {
     #[strum(props(default = "0"))] // also change MediaQuality.default() on changes
     MediaQuality,
 
-    /// Timer in seconds after which the message is deleted from the
-    /// server.
-    ///
-    /// 0 means messages are never deleted by Delta Chat.
-    ///
-    /// Value 1 is treated as "delete at once": messages are deleted
-    /// immediately, without moving to DeltaChat folder.
-    ///
-    /// Default is 1 for chatmail accounts without `BccSelf`, 0 otherwise.
-    DeleteServerAfter,
-
     /// Timer in seconds after which the message is deleted from the
     /// device.
     ///
@@ -565,14 +554,6 @@ impl Context {
         // Default values
         let val = match key {
             Config::ConfiguredInboxFolder => Some("INBOX".to_string()),
-            Config::DeleteServerAfter => {
-                match !Box::pin(self.get_config_bool(Config::BccSelf)).await?
-                    && Box::pin(self.is_chatmail()).await?
-                {
-                    true => Some("1".to_string()),
-                    false => Some("0".to_string()),
-                }
-            }
             Config::Addr => self.get_config_opt(Config::ConfiguredAddr).await?,
             _ => key.get_str("default").map(|s| s.to_string()),
         };
@@ -653,23 +634,6 @@ impl Context {
         self.get_config_bool(Config::MdnsEnabled).await
     }
 
-    /// Gets configured "delete_server_after" value.
-    ///
-    /// `None` means never delete the message, `Some(0)` means delete
-    /// at once, `Some(x)` means delete after `x` seconds.
-    pub async fn get_config_delete_server_after(&self) -> Result<Option<i64>> {
-        let val = match self
-            .get_config_parsed::<i64>(Config::DeleteServerAfter)
-            .await?
-            .unwrap_or(0)
-        {
-            0 => None,
-            1 => Some(0),
-            x => Some(x),
-        };
-        Ok(val)
-    }
-
     /// Gets the configured provider.
     ///
     /// The provider is determined by the current primary transport.