core: fix dev mode genesis difficulty (#29469)

The dev mode is nowadays in Merge-mode from genesis, hence the difficulty of the first block should be zero.

core/genesis.go

@@ -582,7 +582,7 @@ func DeveloperGenesisBlock(gasLimit uint64, faucet *common.Address) *Genesis {
 		Config:     &config,
 		GasLimit:   gasLimit,
 		BaseFee:    big.NewInt(params.InitialBaseFee),
-		Difficulty: big.NewInt(1),
+		Difficulty: big.NewInt(0),
 		Alloc: map[common.Address]types.Account{
 			common.BytesToAddress([]byte{1}): {Balance: big.NewInt(1)}, // ECRecover
 			common.BytesToAddress([]byte{2}): {Balance: big.NewInt(1)}, // SHA256