Fulu update to spec v1.6.0-alpha.4 (#7890)

Fulu update to spec [v1.6.0-alpha.4](https://github.com/ethereum/consensus-specs/releases/tag/v1.6.0-alpha.4).
- Make `number_of_columns` a preset
- Optimise `get_custody_groups` to avoid computing if cgc = 128
- Add support for additional typenum values in type_dispatch macro

beacon_node/network/src/sync/network_context/custody.rs

@@ -13,16 +13,14 @@ use std::collections::HashSet;
 use std::time::{Duration, Instant};
 use std::{collections::HashMap, marker::PhantomData, sync::Arc};
 use tracing::{debug, warn};
-use types::EthSpec;
 use types::{DataColumnSidecar, Hash256, data_column_sidecar::ColumnIndex};
+use types::{DataColumnSidecarList, EthSpec};
 
 use super::{LookupRequestResult, PeerGroup, RpcResponseResult, SyncNetworkContext};
 
 const FAILED_PEERS_CACHE_EXPIRY_SECONDS: u64 = 5;
 const MAX_STALE_NO_PEERS_DURATION: Duration = Duration::from_secs(30);
 
-type DataColumnSidecarList<E> = Vec<Arc<DataColumnSidecar<E>>>;
-
 pub struct ActiveCustodyRequest<T: BeaconChainTypes> {
     block_root: Hash256,
     custody_id: CustodyId,

beacon_node/network/src/sync/network_context/requests/data_columns_by_root.rs

@@ -1,8 +1,8 @@
 use lighthouse_network::rpc::methods::DataColumnsByRootRequest;
+use ssz_types::VariableList;
 use std::sync::Arc;
 use types::{
     ChainSpec, DataColumnSidecar, DataColumnsByRootIdentifier, EthSpec, ForkName, Hash256,
-    RuntimeVariableList,
 };
 
 use super::{ActiveRequestItems, LookupVerifyError};
@@ -14,13 +14,12 @@ pub struct DataColumnsByRootSingleBlockRequest {
 }
 
 impl DataColumnsByRootSingleBlockRequest {
-    pub fn try_into_request(
+    pub fn try_into_request<E: EthSpec>(
         self,
         fork_name: ForkName,
         spec: &ChainSpec,
-    ) -> Result<DataColumnsByRootRequest, &'static str> {
-        let number_of_columns = spec.number_of_columns as usize;
-        let columns = RuntimeVariableList::new(self.indices, number_of_columns)
+    ) -> Result<DataColumnsByRootRequest<E>, &'static str> {
+        let columns = VariableList::new(self.indices)
             .map_err(|_| "Number of indices exceeds total number of columns")?;
         Ok(DataColumnsByRootRequest::new(
             vec![DataColumnsByRootIdentifier {