add `latest_pdu_in_room` timeline function

Signed-off-by: strawberry <strawberry@puppygock.gay>

src/service/rooms/timeline/mod.rs

@@ -82,6 +82,14 @@ impl Service {
 			.transpose()
 	}
 
+	#[tracing::instrument(skip(self))]
+	pub fn latest_pdu_in_room(&self, room_id: &RoomId) -> Result<Option<Arc<PduEvent>>> {
+		self.all_pdus(user_id!("@placeholder:conduwuit.placeholder"), room_id)?
+			.last()
+			.map(|o| o.map(|(_, p)| Arc::new(p)))
+			.transpose()
+	}
+
 	#[tracing::instrument(skip(self))]
 	pub fn last_timeline_count(&self, sender_user: &UserId, room_id: &RoomId) -> Result<PduCount> {
 		self.db.last_timeline_count(sender_user, room_id)