CancelOrder program

[rafaelvanoni]

Hi folks, I'm trying to write a client that issues CancelOrder transactions and it seems that program hasn't been implemented yet. Is that correct? If so, I'd be happy to propose a PR with it.

To clarify, the problem I'm trying to solve is that I can't create a solana.NewTransaction() with a InstructionCancelOrder{} because the latter doesn't fully implement solana.Instruction. It seems that "fully" implementing CancelOrder similarly to what's done in programs/system/CreateAccount.go for example, would solve that.

[aspin]

Just as a follow up for anyone else experiencing this issue: we figured out that the usage is like this:

	// create the CancelOrder instruction
	cancelInstruction := serum.InstructionCancelOrderByClientIdV2{
		ClientID: clientID,
		Accounts: &serum.CancelOrderByClientIdV2Accounts{
			Market:     solana.Meta(marketPk).WRITE(),
			Bids:       solana.Meta(bidsPk).WRITE(),
			Asks:       solana.Meta(asksPk).WRITE(),
			OpenOrders: solana.Meta(openOrdersPk).WRITE(),
			Owner:      solana.Meta(ownerPk).SIGNER(),
			EventQueue: solana.Meta(eventQueuePk).WRITE(),
		},
	}

	serumInstruction := serum.Instruction{
		BaseVariant: bin.BaseVariant{
			TypeID: serum.InstructionDefVariant.TypeID("cancel_order_by_client_id_v2"),
			Impl:   cancelInstruction,
		},
		Version: serumInstructionVersion,
	}

	buf := new(bytes.Buffer)
	err := bin.NewBinEncoder(buf).Encode(serumInstruction)
	if err != nil {
		return nil, fmt.Errorf("failed to encode CancelOrder instruction (%w)", err)
	}
	

	serumV3Dex, _ := solana.PublicKeyFromBase58("9xQeWvG816bUx9EPjHmaT23yvVM2ZWbrrpZb9PusVFin")
	instruction := &solana.GenericInstruction{
		AccountValues: []*solana.AccountMeta{
			cancelInstruction.Accounts.Market,
			cancelInstruction.Accounts.Bids,
			cancelInstruction.Accounts.Asks,
			cancelInstruction.Accounts.OpenOrders,
			cancelInstruction.Accounts.Owner,
			cancelInstruction.Accounts.EventQueue,
		},
		ProgID:    serumV3Dex,
		DataBytes: buf.Bytes(),
	}