fix: Add tolerance to MemberListTimestamp (#5366)

Let's add a 1-minute tolerance to `Params::MemberListTimestamp`.

This adds to the group membership consistency algo the following properties:
- If remote group membership changes were made by two members in parallel, both of them are applied,
  no matter in which order the messages are received.
- If we remove a member locally, only explicit remote member additions/removals made in parallel are
  allowed, but not the synchronisation of the member list from "To". Before, if somebody managed to
  reply earlier than receiving our removal of a member, we added it back which doesn't look good.

src/mimeparser.rs

@@ -15,7 +15,7 @@ use crate::aheader::{Aheader, EncryptPreference};
 use crate::blob::BlobObject;
 use crate::chat::{add_info_msg, ChatId};
 use crate::config::Config;
-use crate::constants::{Chattype, DC_DESIRED_TEXT_LINES, DC_DESIRED_TEXT_LINE_LEN};
+use crate::constants::{self, Chattype, DC_DESIRED_TEXT_LINES, DC_DESIRED_TEXT_LINE_LEN};
 use crate::contact::{addr_cmp, addr_normalize, Contact, ContactId, Origin};
 use crate::context::Context;
 use crate::decrypt::{
@@ -212,7 +212,9 @@ impl MimeMessage {
             .headers
             .get_header_value(HeaderDef::Date)
             .and_then(|v| mailparse::dateparse(&v).ok())
-            .map_or(timestamp_rcvd, |value| min(value, timestamp_rcvd + 60));
+            .map_or(timestamp_rcvd, |value| {
+                min(value, timestamp_rcvd + constants::TIMESTAMP_SENT_TOLERANCE)
+            });
         let mut hop_info = parse_receive_headers(&mail.get_headers());
 
         let mut headers = Default::default();