Deneb review common/eth2 (#4698)

* Update comments and small cleanup.

* Deserialize into `SsePayloadAttributesV3` for Deneb fork. Update `SignedBlockContents::blobs_cloned` to return blobs for `BlindedBlockAndBlobSidecars`.

* Improve code readability and error handling when converting blinded block into full block.

beacon_node/http_api/src/lib.rs

@@ -1729,7 +1729,7 @@ pub fn serve<T: BeaconChainTypes>(
         );
 
     /*
-     * beacon/blobs
+     * beacon/blob_sidecars
      */
 
     // GET beacon/blob_sidecars/{block_id}

beacon_node/http_api/src/publish_blocks.rs

@@ -373,8 +373,8 @@ pub async fn reconstruct_block<T: BeaconChainTypes>(
             .try_into_full_block_and_blobs(Some(full_payload_contents))
             .map(ProvenancedBlock::builder),
     }
-    .ok_or_else(|| {
-        warp_utils::reject::custom_server_error("Unable to add payload to block".to_string())
+    .map_err(|e| {
+        warp_utils::reject::custom_server_error(format!("Unable to add payload to block: {e:?}"))
     })
 }