fix: Properly sync left rooms

- Remove most usages of `update_membership` in favor
  of directly calling the `mark_as_*` functions
- Store the leave membership event as the value in the
  `userroomid_leftstate` table
- Use the `userroomid_leftstate` table to synchronize the
  timeline and state for left rooms if possible

src/api/client/sync/mod.rs

@@ -4,15 +4,15 @@ mod v5;
 use std::collections::VecDeque;
 
 use conduwuit::{
-	PduCount, Result,
+	Event, PduCount, Result,
 	matrix::pdu::PduEvent,
-	trace,
+	ref_at, trace,
 	utils::stream::{BroadbandExt, ReadyExt, TryIgnore},
 };
 use conduwuit_service::Services;
 use futures::StreamExt;
 use ruma::{
-	RoomId, UserId,
+	OwnedUserId, RoomId, UserId,
 	events::TimelineEventType::{
 		self, Beacon, CallInvite, PollStart, RoomEncrypted, RoomMessage, Sticker,
 	},
@@ -29,6 +29,16 @@ pub(crate) struct TimelinePdus {
 	pub limited: bool,
 }
 
+impl TimelinePdus {
+	fn senders(&self) -> impl Iterator<Item = OwnedUserId> {
+		self.pdus
+			.iter()
+			.map(ref_at!(1))
+			.map(Event::sender)
+			.map(Into::into)
+	}
+}
+
 async fn load_timeline(
 	services: &Services,
 	sender_user: &UserId,