Use mock web3/powchain for fuzz test (#8866)

* Use mock web3/powchain for fuzz test

* gofmt

* build viz

beacon-chain/powchain/testing/BUILD.bazel

@@ -8,7 +8,10 @@ go_library(
         "mock_powchain.go",
     ],
     importpath = "github.com/prysmaticlabs/prysm/beacon-chain/powchain/testing",
-    visibility = ["//beacon-chain:__subpackages__"],
+    visibility = [
+        "//beacon-chain:__subpackages__",
+        "//fuzz:__pkg__",
+    ],
     deps = [
         "//beacon-chain/powchain/types:go_default_library",
         "//beacon-chain/state/interface:go_default_library",

fuzz/BUILD.bazel

@@ -75,6 +75,7 @@ go_fuzz_test(
         "//beacon-chain/blockchain:go_default_library",
         "//beacon-chain/operations/slashings:go_default_library",
         "//beacon-chain/forkchoice/protoarray:go_default_library",
+        "//beacon-chain/powchain/testing:go_default_library",
         "//shared/testutil:go_default_library",
         "@com_github_libp2p_go_libp2p_core//peer:go_default_library",
         "@com_github_libp2p_go_libp2p_pubsub//:go_default_library",

fuzz/block_fuzz.go

@@ -24,6 +24,7 @@ import (
 	"github.com/prysmaticlabs/prysm/beacon-chain/operations/voluntaryexits"
 	"github.com/prysmaticlabs/prysm/beacon-chain/p2p"
 	p2pt "github.com/prysmaticlabs/prysm/beacon-chain/p2p/testing"
+	powt "github.com/prysmaticlabs/prysm/beacon-chain/powchain/testing"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state/stateV0"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state/stategen"
 	"github.com/prysmaticlabs/prysm/beacon-chain/sync"
@@ -133,7 +134,7 @@ func BeaconFuzzBlock(b []byte) {
 	}
 
 	chain, err := blockchain.NewService(context.Background(), &blockchain.Config{
-		ChainStartFetcher: nil,
+		ChainStartFetcher: powt.NewPOWChain(),
 		BeaconDB:          db1,
 		DepositCache:      nil,
 		AttPool:           ap,