feat(opsim): create depositTx subscriber

[jakim929]

• SubscribeDepositTx creates a subscription to depositTransactions given a chain api and the deposit contract address. under the hood it transforms the event log subscription
• adds chainapi package, which is the interface that chains should expose to opsim
• adds some testutils MockChain which can be overridden with methods for testing

this is not used anywhere right now, but will be used in a separate PR once we figure out how to get bridge contracts deployed on the L1

it will be used like below

func (opSim *OpSimulator) StartDepositProcessor(ctx context.Context) error {
	depositTxCh := make(chan *types.DepositTx)

	sub, err := SubscribeDepositTx(ctx, opSim.l1Chain, depositContractAddr, depositTxCh)

	if err != nil {
		return fmt.Errorf("failed to start deposit processor: %w", err)
	}

	go func() {
		for {
			select {
			case dep := <-depositTxCh:
				if err := opSim.l2Chain.EthSendTransaction(ctx, types.NewTx(dep)); err != nil {
					opSim.log.Error("failed to submit deposit tx: %w", err)
				}
			case <-ctx.Done():
				sub.Unsubscribe()
				close(depositTxCh)
				return
			}
		}
	}()

	return nil
}

[jakim929]

• feat(opsim): create depositTx subscriber #45 👈
• main

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[tremarkley]

this all looks great to me, but I would probably wait on a review from @nitaliano or @hamdiallam before merging

[nitaliano]

nice!