use block ID vs full block in LC data caching (#3741)

`cacheLightClientData` does not need full block data, pass just ID.

beacon_chain/consensus_object_pools/blockchain_dag_light_client.nim

@@ -153,14 +153,11 @@ proc getLightClientData(
   try: dag.lightClientCache.data[bid]
   except KeyError: raiseAssert "Unreachable"
 
-proc cacheLightClientData*(
-    dag: ChainDAGRef,
-    state: HashedBeaconStateWithSyncCommittee,
-    blck: TrustedSignedBeaconBlockWithSyncAggregate) =
+proc cacheLightClientData(
+    dag: ChainDAGRef, state: HashedBeaconStateWithSyncCommittee, bid: BlockId) =
   ## Cache data for a given block and its post-state to speed up creating future
   ## `LightClientUpdate` and `LightClientBootstrap` instances that refer to this
   ## block and state.
-  let bid = BlockId(root: blck.root, slot: blck.message.slot)
   var cachedData {.noinit.}: CachedLightClientData
   state.data.build_proof(
     altair.CURRENT_SYNC_COMMITTEE_INDEX,
@@ -352,10 +349,10 @@ proc processNewBlockForLightClient*(
     return
 
   when signedBlock is bellatrix.TrustedSignedBeaconBlock:
-    dag.cacheLightClientData(state.bellatrixData, signedBlock)
+    dag.cacheLightClientData(state.bellatrixData, signedBlock.toBlockId())
     dag.createLightClientUpdates(state.bellatrixData, signedBlock, parentBid)
   elif signedBlock is altair.TrustedSignedBeaconBlock:
-    dag.cacheLightClientData(state.altairData, signedBlock)
+    dag.cacheLightClientData(state.altairData, signedBlock.toBlockId())
     dag.createLightClientUpdates(state.altairData, signedBlock, parentBid)
   elif signedBlock is phase0.TrustedSignedBeaconBlock:
     raiseAssert "Unreachable" # `earliestSlot` cannot be before Altair
@@ -720,7 +717,7 @@ proc initLightClientCache*(dag: ChainDAGRef) =
       withStateAndBlck(state, bdata):
         when stateFork >= BeaconStateFork.Altair:
           # Cache light client data (non-finalized blocks may refer to this)
-          dag.cacheLightClientData(state, blck)
+          dag.cacheLightClientData(state, blck.toBlockId())
 
           # Create `LightClientUpdate` instances
           if bid.slot != lowSlot: