Address review comments and fix lint.

Author: jimmygchen

beacon_node/beacon_chain/src/test_utils.rs

@@ -2085,7 +2085,7 @@ where
                 })
                 .transpose()
                 .expect("should convert blobs to columns")
-                .unwrap_or(vec![]);
+                .unwrap_or_default();
             RpcBlock::new_with_custody_columns(Some(block_root), block, columns, &self.spec)?
         } else {
             let blobs = blob_items

beacon_node/network/src/service.rs

@@ -789,6 +789,11 @@ impl<T: BeaconChainTypes> NetworkService<T> {
     /// 1. Data column subscription logic depends on subscription configuration.
     /// 2. Data column topic subscriptions will be dynamic based on validator balances due to
     ///    validator custody.
+    ///
+    /// TODO(das): The downside with not including it in core fork topic is - we subscribe to
+    /// PeerDAS topics on startup if Fulu is scheduled, rather than waiting until the fork.
+    /// If this is an issue we could potentially consider adding the logic to
+    /// `network.subscribe_new_fork_topics()`.
     fn subscribe_to_peer_das_topics(&mut self, subscribed_topics: &mut Vec<GossipTopic>) {
         let column_subnets_to_subscribe = if self.subscribe_all_data_column_subnets {
             Cow::Owned(