Instrument publish_block code path (#7945)

Instrument `publish_block` code path and log dropped data columns when publishing.

Example spans (running the devnet from my laptop, so the numbers aren't great)

<img width="734" height="296" alt="image" src="https://github.com/user-attachments/assets/20620bf7-2b38-4392-aa75-9ba96d3a7f0d" />

<img width="718" height="625" alt="image" src="https://github.com/user-attachments/assets/61e1ff1c-65b5-4ad4-981a-d0fadc9829e1" />

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -3059,6 +3059,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
 
     /// Cache the data columns in the processing cache, process it, then evict it from the cache if it was
     /// imported or errors.
+    #[instrument(skip_all, level = "debug")]
     pub async fn process_gossip_data_columns(
         self: &Arc<Self>,
         data_columns: Vec<GossipVerifiedDataColumn<T>>,