Fix correctness issues in single-block lookup state machine

- add_peer: replace !=-vs-|= typo so Gloas child-peer additions actually
  propagate back through add_peers_to_lookup_and_ancestors and kick
  continue_requests.
- data_peer_group: return the PeerGroup stored in DataRequestState
  Downloaded/Processing instead of todo!(), so InvalidColumn attribution
  in mod.rs no longer panics on a live error path.
- Restore the original `parent_root != ZERO` guard for the parent-known
  check; the genesis block has no real parent so it must fall through to
  processing rather than panic (was todo!()) or be dropped as Failed.
- Wire envelope_is_known_to_fork_choice as a NoRequestNeeded short-
  circuit at the top of payload_lookup_request.
- Rename gload_child_peers -> gloas_child_peers (typo).
- Drop DataDownloadKind, peek_downloaded_peer_group, DataRequest.slot,
  DownloadedData::Blobs.expected_blobs — all dead per the compiler.
- Update test helpers to send UnknownParentSidecarHeader so the lookup
  test suite compiles and runs under the new manager API.

Tests: phase0 79/79, electra 59/59, fulu 59/59.

beacon_node/network/src/sync/network_context.rs

@@ -955,6 +955,14 @@ impl<T: BeaconChainTypes> SyncNetworkContext<T> {
         lookup_peers: Arc<RwLock<HashSet<PeerId>>>,
         block_root: Hash256,
     ) -> Result<LookupRequestResult, RpcRequestSendError> {
+        // Skip the download if fork-choice already saw this envelope (e.g. imported via gossip
+        // before the lookup got here).
+        if self.chain.envelope_is_known_to_fork_choice(&block_root) {
+            return Ok(LookupRequestResult::NoRequestNeeded(
+                "envelope already known to fork-choice",
+            ));
+        }
+
         let active_request_count_by_peer = self.active_request_count_by_peer();
         let Some(peer_id) = lookup_peers
             .read()