Validator custody: Update to the latest specification. (#15532)

* Validator custody: Update to the latest specfication.

* Update beacon-chain/blockchain/process_block.go

Co-authored-by: terence <terence@prysmaticlabs.com>

* Fix James' comment.

* Fix James' comment.

* Fix James' comment.

---------

Co-authored-by: terence <terence@prysmaticlabs.com>
Co-authored-by: james-prysm <90280386+james-prysm@users.noreply.github.com>

testing/spectest/shared/common/forkchoice/BUILD.bazel

@@ -25,6 +25,7 @@ go_library(
         "//beacon-chain/forkchoice:go_default_library",
         "//beacon-chain/forkchoice/doubly-linked-tree:go_default_library",
         "//beacon-chain/operations/attestations:go_default_library",
+        "//beacon-chain/p2p/testing:go_default_library",
         "//beacon-chain/startup:go_default_library",
         "//beacon-chain/state:go_default_library",
         "//beacon-chain/state/state-native:go_default_library",

testing/spectest/shared/common/forkchoice/service.go

@@ -16,6 +16,7 @@ import (
 	"github.com/OffchainLabs/prysm/v6/beacon-chain/forkchoice"
 	doublylinkedtree "github.com/OffchainLabs/prysm/v6/beacon-chain/forkchoice/doubly-linked-tree"
 	"github.com/OffchainLabs/prysm/v6/beacon-chain/operations/attestations"
+	p2pTesting "github.com/OffchainLabs/prysm/v6/beacon-chain/p2p/testing"
 	"github.com/OffchainLabs/prysm/v6/beacon-chain/startup"
 	"github.com/OffchainLabs/prysm/v6/beacon-chain/state"
 	"github.com/OffchainLabs/prysm/v6/beacon-chain/state/stategen"
@@ -82,6 +83,7 @@ func startChainService(t testing.TB,
 		blockchain.WithDataColumnStorage(filesystem.NewEphemeralDataColumnStorage(t)),
 		blockchain.WithSyncChecker(mock.MockChecker{}),
 		blockchain.WithGenesisTime(genesis),
+		blockchain.WithP2PBroadcaster(&p2pTesting.TestP2P{}),
 	)
 	service, err := blockchain.NewService(t.Context(), opts...)
 	require.NoError(t, err)