[WIP] feat: use json-iterator replace encoding/json for performance

[ohko4711]

1. use json-iterator 100% compatibility with standard lib
2. To avoid conflicts with json in the existing code, jsonIter is used instead.

tested with erigon's Genesis struct:

./gencodec -dir ./erigon-lib/types -type Genesis  -out gen_genesis-new.go

// Code generated by github.com/fjl/gencodec. DO NOT EDIT.

package types

import (
	"errors"
	"math/big"

	"github.com/erigontech/erigon-lib/chain"
	"github.com/erigontech/erigon-lib/common"
	jsoniter "github.com/json-iterator/go"
)

var jsonIter = jsoniter.ConfigCompatibleWithStandardLibrary

// MarshalJSON marshals as JSON.
func (g Genesis) MarshalJSON() ([]byte, error) {
	type Genesis struct {
		Config                *chain.Config  `json:"config"`
		Nonce                 uint64         `json:"nonce"`
		Timestamp             uint64         `json:"timestamp"`
		ExtraData             []byte         `json:"extraData"`
		GasLimit              uint64         `json:"gasLimit"   gencodec:"required"`
		Difficulty            *big.Int       `json:"difficulty" gencodec:"required"`
		Mixhash               common.Hash    `json:"mixHash"`
		Coinbase              common.Address `json:"coinbase"`
		Alloc                 GenesisAlloc   `json:"alloc"      gencodec:"required"`
		AuRaSeal              *AuRaSeal      `json:"seal"`
		Number                uint64         `json:"number"`
		GasUsed               uint64         `json:"gasUsed"`
		ParentHash            common.Hash    `json:"parentHash"`
		BaseFee               *big.Int       `json:"baseFeePerGas"`
		BlobGasUsed           *uint64        `json:"blobGasUsed"`
		ExcessBlobGas         *uint64        `json:"excessBlobGas"`
		ParentBeaconBlockRoot *common.Hash   `json:"parentBeaconBlockRoot"`
		RequestsHash          *common.Hash   `json:"requestsHash"`
	}
	var enc Genesis
	enc.Config = g.Config
	enc.Nonce = g.Nonce
	enc.Timestamp = g.Timestamp
	enc.ExtraData = g.ExtraData
	enc.GasLimit = g.GasLimit
	enc.Difficulty = g.Difficulty
	enc.Mixhash = g.Mixhash
	enc.Coinbase = g.Coinbase
	enc.Alloc = g.Alloc
	enc.AuRaSeal = g.AuRaSeal
	enc.Number = g.Number
	enc.GasUsed = g.GasUsed
	enc.ParentHash = g.ParentHash
	enc.BaseFee = g.BaseFee
	enc.BlobGasUsed = g.BlobGasUsed
	enc.ExcessBlobGas = g.ExcessBlobGas
	enc.ParentBeaconBlockRoot = g.ParentBeaconBlockRoot
	enc.RequestsHash = g.RequestsHash
	return jsonIter.Marshal(&enc)
}

// UnmarshalJSON unmarshals from JSON.
func (g *Genesis) UnmarshalJSON(input []byte) error {
	type Genesis struct {
		Config                *chain.Config   `json:"config"`
		Nonce                 *uint64         `json:"nonce"`
		Timestamp             *uint64         `json:"timestamp"`
		ExtraData             []byte          `json:"extraData"`
		GasLimit              *uint64         `json:"gasLimit"   gencodec:"required"`
		Difficulty            *big.Int        `json:"difficulty" gencodec:"required"`
		Mixhash               *common.Hash    `json:"mixHash"`
		Coinbase              *common.Address `json:"coinbase"`
		Alloc                 *GenesisAlloc   `json:"alloc"      gencodec:"required"`
		AuRaSeal              *AuRaSeal       `json:"seal"`
		Number                *uint64         `json:"number"`
		GasUsed               *uint64         `json:"gasUsed"`
		ParentHash            *common.Hash    `json:"parentHash"`
		BaseFee               *big.Int        `json:"baseFeePerGas"`
		BlobGasUsed           *uint64         `json:"blobGasUsed"`
		ExcessBlobGas         *uint64         `json:"excessBlobGas"`
		ParentBeaconBlockRoot *common.Hash    `json:"parentBeaconBlockRoot"`
		RequestsHash          *common.Hash    `json:"requestsHash"`
	}
	var dec Genesis
	if err := jsonIter.Unmarshal(input, &dec); err != nil {
		return err
	}
	if dec.Config != nil {
		g.Config = dec.Config
	}
	if dec.Nonce != nil {
		g.Nonce = *dec.Nonce
	}
	if dec.Timestamp != nil {
		g.Timestamp = *dec.Timestamp
	}
	if dec.ExtraData != nil {
		g.ExtraData = dec.ExtraData
	}
	if dec.GasLimit == nil {
		return errors.New("missing required field 'gasLimit' for Genesis")
	}
	g.GasLimit = *dec.GasLimit
	if dec.Difficulty == nil {
		return errors.New("missing required field 'difficulty' for Genesis")
	}
	g.Difficulty = dec.Difficulty
	if dec.Mixhash != nil {
		g.Mixhash = *dec.Mixhash
	}
	if dec.Coinbase != nil {
		g.Coinbase = *dec.Coinbase
	}
	if dec.Alloc == nil {
		return errors.New("missing required field 'alloc' for Genesis")
	}
	g.Alloc = *dec.Alloc
	if dec.AuRaSeal != nil {
		g.AuRaSeal = dec.AuRaSeal
	}
	if dec.Number != nil {
		g.Number = *dec.Number
	}
	if dec.GasUsed != nil {
		g.GasUsed = *dec.GasUsed
	}
	if dec.ParentHash != nil {
		g.ParentHash = *dec.ParentHash
	}
	if dec.BaseFee != nil {
		g.BaseFee = dec.BaseFee
	}
	if dec.BlobGasUsed != nil {
		g.BlobGasUsed = dec.BlobGasUsed
	}
	if dec.ExcessBlobGas != nil {
		g.ExcessBlobGas = dec.ExcessBlobGas
	}
	if dec.ParentBeaconBlockRoot != nil {
		g.ParentBeaconBlockRoot = dec.ParentBeaconBlockRoot
	}
	if dec.RequestsHash != nil {
		g.RequestsHash = dec.RequestsHash
	}
	return nil
}