feat: verify message and verify transaction

[wuuuk]

Fixes #12

Changes:

• Move signer.IntentScope to constant package
• Move the intent function in the signer to the models package
• Signer: add transaction signature and message signature of sui protocol
• Models: add signature verification of transaction and message

Examples:

• Sign message

func main() {
	user, _ := NewSignertWithMnemonic("${MNEMONIC_STRING}")

	// sign message
	message := "Welcome to SUI!"
	signature, _ := user.SignPersonalMessage(message)

	// verify message
	signer, pass, err := models.VerifyPersonalMessage(message, signature.Signature)
	...
}

• Sign transaction

func main() {
	user, _ := NewSignertWithMnemonic("${MNEMONIC_STRING}")
	suiApi := sui.NewSuiClient("${RPC_URL}")

	// move call
	txn, _ := suiApi.MoveCall(context.Background(), models.MoveCallRequest{})

	// sign transaction
	signature, _ := user.SignTransaction(txn.TxBytes)

	// verify transaction
	signer, pass, err := models.VerifyTransaction(txn.TxBytes, signature.Signature)
	// ...
}