Check DKIM Authentication-Results (#3583)

Fix #3507

Note that this is not intended for a release at this point! We first have to test whether it runs stable enough. If we want to make a release while we are not confident enough in authres-checking, then we have to disable it.

BTW, most of the 3000 new lines are in `test_data/messages/dkimchecks...`, not the actual code

da3a4b94 adds the results to the Message info. It currently does this by adding them to `hop_info`. Maybe we should rename `hop_info` to `extra_info` or something; this has the disadvantage that we can't rename the sql column name though.

Follow-ups for this could be:
- In `update_authservid_candidates()`: Implement the rest of the algorithm @hpk42 and me thought about. What's missing is remembering how sure we are that these are the right authserv-ids. Esp., when receiving a message sent from another account at the same domain, we can be quite sure that the authserv-ids in there are the ones of our email server. This will make authres-checking work with buzon.uy, disroot.org, yandex.ru, mailo.com, and riseup.net.
- Think about how we present this to the user - e.g. currently the only change is that we don't accept key changes, which will mean that the small lock on the message is not shown.
- And it will mean that we can fully enable AEAP, after revisiting the security implications of this, and assuming everyone (esp. @link2xt who pointed out the problems in the first place) feels comfortable with it.

src/imex.rs

@@ -6,7 +6,7 @@ use std::path::{Path, PathBuf};
 
 use ::pgp::types::KeyTrait;
 use anyhow::{bail, ensure, format_err, Context as _, Result};
-use futures::{StreamExt, TryStreamExt};
+use futures::StreamExt;
 use futures_lite::FutureExt;
 use rand::{thread_rng, Rng};
 use tokio::fs::{self, File};
@@ -17,7 +17,6 @@ use crate::chat::{self, delete_and_reset_all_device_msgs, ChatId};
 use crate::config::Config;
 use crate::contact::ContactId;
 use crate::context::Context;
-use crate::e2ee;
 use crate::events::EventType;
 use crate::key::{self, DcKey, DcSecretKey, SignedPublicKey, SignedSecretKey};
 use crate::log::LogExt;
@@ -31,6 +30,7 @@ use crate::tools::{
     create_folder, delete_file, get_filesuffix_lc, open_file_std, read_file, time, write_file,
     EmailAddress,
 };
+use crate::{e2ee, tools};
 
 // Name of the database file in the backup.
 const DBFILE_BACKUP_NAME: &str = "dc_database_backup.sqlite";
@@ -576,10 +576,7 @@ async fn export_backup_inner(
         .append_path_with_name(temp_db_path, DBFILE_BACKUP_NAME)
         .await?;
 
-    let read_dir: Vec<_> =
-        tokio_stream::wrappers::ReadDirStream::new(fs::read_dir(context.get_blobdir()).await?)
-            .try_collect()
-            .await?;
+    let read_dir = tools::read_dir(context.get_blobdir()).await?;
     let count = read_dir.len();
     let mut written_files = 0;