Fix beacon-chain and network test failures under FORK_NAME=gloas/fulu

- block_verification: skip ParentEnvelopeUnknown check when parent is the
  proto-array anchor. The anchor's `payload_received` is intentionally
  false per spec (never added to `store.payloads`), but no envelope is
  expected for it; without this exception the check rejects every
  post-anchor gloas block.

- network tests: disable `engineGetBlobs` in the TestRig harness. Under
  real crypto the mock EL's blob fetch raced the gossip path, importing
  via a spawned task that the test didn't await -- leaving `head_root()`
  unchanged when the assertion ran. The tests are designed to exercise
  the gossip + data-column path; the engine fetch was incidental.

- network tests: relax `data_column_reconstruction_at_deadline` to allow
  trailing duplicate reconstruction work items. The reprocess queue
  removes its dedup entry on dispatch, so a column processed during an
  in-flight reconstruction can dispatch a second one. The second is a
  no-op via `reconstruction_started`, so accept >= 1 trailing event.

beacon_node/beacon_chain/src/block_verification.rs

@@ -942,12 +942,18 @@ impl<T: BeaconChainTypes> GossipVerifiedBlock<T> {
 
         // Check that we've received the parent envelope. If not, issue a single envelope
         // lookup for the parent and queue this block in the reprocess queue.
+        //
+        // The anchor block (proto-array root) is implicitly considered to have its payload
+        // received: there is no envelope to fetch for the anchor (per spec, the anchor is
+        // never added to `store.payloads`), and the anchor is trusted by definition.
         let parent_is_gloas = chain
             .spec
             .fork_name_at_slot::<T::EthSpec>(parent_block.slot)
             .gloas_enabled();
+        let parent_is_anchor = parent_block.parent_root.is_none();
 
         if parent_is_gloas
+            && !parent_is_anchor
             && !fork_choice_read_lock.is_payload_received(&block.message().parent_root())
         {
             return Err(BlockError::ParentEnvelopeUnknown {