Allow optimistic payload verification for GLOaS envelopes

Remove the OptimisticSyncNotSupported check in into_executed_payload_envelope.
When the EL returns SYNCING (optimistic) for a payload envelope's newPayload
call, the envelope import should proceed rather than being rejected. This
commonly occurs after range sync imports blocks that the EL hasn't yet
validated - subsequent envelopes arriving via gossip would be rejected because
the EL is still catching up.

The downstream import path already handles optimistic status correctly:
- fork choice marks the payload as received regardless of EL status
- the payload_verification_status is propagated to SSE events/metrics
- if the payload is later found invalid, the normal invalidation mechanism
  handles it (same as for blocks)

beacon_node/beacon_chain/src/payload_envelope_verification/import.rs

@@ -192,13 +192,11 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
             .map_err(BeaconChainError::TokioJoin)?
             .ok_or(BeaconChainError::RuntimeShutdown)??;
 
-        // TODO(gloas): optimistic sync is not supported for Gloas, maybe we could re-add it
+        // NOTE: We allow optimistic (SYNCING) payload verification status here.
-        if payload_verification_outcome
+        // This can happen when the EL is still catching up (e.g., after range sync imports
-            .payload_verification_status
+        // blocks that the EL hasn't validated yet). The envelope import will proceed and
-            .is_optimistic()
+        // fork choice will mark the payload as received. If the payload is later found to
-        {
+        // be invalid, the normal invalidation mechanism will handle it.
-            return Err(BlockError::OptimisticSyncNotSupported { block_root });
-        }
 
         Ok(AvailabilityPendingExecutedEnvelope::new(
             signed_envelope,