feat: new group consistency algorithm

This implements new group consistency algorithm described in
<https://github.com/deltachat/deltachat-core-rust/issues/6401>

New `Chat-Group-Member-Timestamps` header is added
to send timestamps of member additions and removals.
Member is part of the chat if its addition timestamp
is greater or equal to the removal timestamp.

src/contact.rs

@@ -114,7 +114,8 @@ impl ContactId {
                  SET gossiped_timestamp=0
                  WHERE EXISTS (SELECT 1 FROM chats_contacts
                                WHERE chats_contacts.chat_id=chats.id
-                               AND chats_contacts.contact_id=?)",
+                               AND chats_contacts.contact_id=?
+                               AND chats_contacts.add_timestamp >= chats_contacts.remove_timestamp)",
                 (self,),
             )
             .await?;