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/beacon_chain/tests/events.rs

@@ -162,7 +162,7 @@ async fn data_column_sidecar_event_on_process_rpc_columns() {
     // load the precomputed column sidecar to avoid computing them for every block in the tests.
     let mut sidecar = RuntimeVariableList::<DataColumnSidecar<E>>::from_ssz_bytes(
         TEST_DATA_COLUMN_SIDECARS_SSZ,
-        spec.number_of_columns as usize,
+        E::number_of_columns(),
     )
     .unwrap()[0]
         .clone();