refactor: work on search

src/database/key_value/rooms/metadata.rs

@@ -0,0 +1,16 @@
+impl service::room::metadata::Data for KeyValueDatabase {
+    fn exists(&self, room_id: &RoomId) -> Result<bool> {
+        let prefix = match self.get_shortroomid(room_id)? {
+            Some(b) => b.to_be_bytes().to_vec(),
+            None => return Ok(false),
+        };
+
+        // Look for PDUs in that room.
+        Ok(self
+            .pduid_pdu
+            .iter_from(&prefix, false)
+            .next()
+            .filter(|(k, _)| k.starts_with(&prefix))
+            .is_some())
+    }
+}