Add members to chats in a single sql transation (#3780)

This esp. speeds up receive_imf a bit when we recreate the member list (recreate_member_list == true).

It's a preparation for https://github.com/deltachat/deltachat-core-rust/issues/3768, which will be a one-line-fix, but recreate the member list more often, so that we want to optimize this case a bit.

It also adds a benchmark for this case. It's not that easy to make the benchmark non-flaky, but by closing all other programs and locking the CPU to 1.5GHz it worked. It is consistently a few percent faster than ./without-optim:

```
Receive messages/Receive 100 Chat-Group-Member-{Added|Removed} messages                                                                            
                        time:   [52.257 ms 52.569 ms 52.941 ms]
                        change: [-3.5301% -2.6181% -1.6697%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 7 outliers among 100 measurements (7.00%)
  4 (4.00%) high mild
  3 (3.00%) high severe
```

src/securejoin/bob.rs

@@ -60,7 +60,7 @@ pub(super) async fn start_protocol(context: &Context, invite: QrInvite) -> Resul
             // TODO: how does this group become usable?
             let group_chat_id = state.joining_chat_id(context).await?;
             if !is_contact_in_chat(context, group_chat_id, invite.contact_id()).await? {
-                chat::add_to_chat_contacts_table(context, group_chat_id, invite.contact_id())
+                chat::add_to_chat_contacts_table(context, group_chat_id, &[invite.contact_id()])
                     .await?;
             }
             let msg = stock_str::secure_join_started(context, invite.contact_id()).await;