Use short reason strings can save gas

[code423n4]

Handle

WatchPug

Vulnerability details

Every reason string takes at least 32 bytes.

Use short reason strings that fits in 32 bytes or it will become more expensive.

Instances include:

https://github.com/code-423n4/2021-11-bootfinance/blob/f102ee73eb320532c5a7c1e833f225c479577e39/customswap/contracts/Swap.sol#L149-L150

require(_pooledTokens.length == 2, "_pooledTokens.length must be 2 in length");
require(decimals.length == 2, "decimals.length must be 2 in length");

https://github.com/code-423n4/2021-11-bootfinance/blob/f102ee73eb320532c5a7c1e833f225c479577e39/vesting/contracts/Vesting.sol#L196-L197

require(amount > 0, "Claimable amount must be positive");
require(amount <= benTotal[msg.sender], "Cannot withdraw more than total vested amount");

https://github.com/code-423n4/2021-11-bootfinance/blob/f102ee73eb320532c5a7c1e833f225c479577e39/customswap/contracts/SwapUtils.sol#L1677-L1680

require(
    futureA2_ >= 0 && futureA2_ <= MAX_A,
    "futureA2_ must be >= 0 and <= MAX_A"
);

[chickenpie347]

Duplicate of #23