ValidateCoinsForZone can be more efficient

[joe-bowman]

func (z *Zone) ValidateCoinsForZone(coins sdk.Coins) error {
	zoneVals := z.GetValidatorsAddressesAsSlice()

COINS:
	for _, coin := range coins.Sort() {
		if coin.Denom == z.BaseDenom {
			continue
		}

		for _, v := range zoneVals {
			if strings.HasPrefix(coin.Denom, v) {
				// continue 2 levels
				continue COINS
			}
		}
		return fmt.Errorf("invalid denom for zone: %s", coin.Denom)

	}
	return nil
}

for coins containing multiple coins, we could end up iterating over the entire validatorset (which may be hundreds of validators in length) multiple times. Converting zoneVals into map[string]bool will allow us to lookup the validators with a single iteration of the valset (because the change in lsm denom type means we can now split on '/', and thus conduct a simple lookup against the map).

[Dhoni77]

Hi @joe-bowman I would like to work on this

[joe-bowman]

Please feel free to!