Gas Optimizations

[code423n4]

Issue: Variables should not be initialized to their default values
Explanation: Initializing variables to their default values is unnecessary and costs gas

https://github.com/code-423n4/2022-05-runes/blob/060b4f82b79c8308fe65674a39a07c44fa586cd3/contracts/ForgottenRunesWarriorsGuild.sol#L24

    uint256 public numMinted = 0;					

Change 'uint256 public numMinted;' to 'uint256 public numMinted;'

Issue: Require message too long
Explanation: The require message below can be shortened to 32 characters or fewer (as shown) to save gas

https://github.com/code-423n4/2022-05-runes/blob/060b4f82b79c8308fe65674a39a07c44fa586cd3/contracts/ForgottenRunesWarriorsMinter.sol#L148

            'Ether value sent is not sufficient'						

Change message to Ether value sent is insufficient

Multiple issues

There are three opportunities to save gas in each of the two identical code blocks below:

1. Use != 0 instead of > 0 because > 0 costs more gas and numWarriors cannot be < zero (since it is a unit)
2. Divide the require into two separate require messages instead of using '&&'
3. Shorten the require message to 32 characters or fewer

https://github.com/code-423n4/2022-05-runes/blob/060b4f82b79c8308fe65674a39a07c44fa586cd3/contracts/ForgottenRunesWarriorsMinter.sol#L140-L143

https://github.com/code-423n4/2022-05-runes/blob/060b4f82b79c8308fe65674a39a07c44fa586cd3/contracts/ForgottenRunesWarriorsMinter.sol#L210-L213

        require(
            numWarriors > 0 && numWarriors <= 20,
            'You can summon no more than 20 Warriors at a time'
        );					

Change to:

       require(numWarriors != 0, 'Number of Warriors must exceed 0');
       require(numWarriors <= 20, 'Summon <= 20 Warriors at a time');