feat(base): Faster Store::rooms_filtered.

Just like in matrix-org#3552,
this patch updates `Store::rooms_filtered` to not call `Store::room` so
that it doesn't lock `rooms` for each item, thus making it way faster.

crates/matrix-sdk-base/src/store/mod.rs

@@ -213,8 +213,8 @@ impl Store {
             .read()
             .unwrap()
             .iter()
-            .filter(|(_, r)| filter.matches(r.state()))
-            .filter_map(|(id, _)| self.get_room(id))
+            .filter(|(_, room)| filter.matches(room.state()))
+            .map(|(_, room)| room.clone())
             .collect()
     }