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-nested/blob/f646002b692ca5fa3631acfff87dda897541cf41/contracts/NestedFactory.sol#L84-L84

require(i > 0, "NestedFactory::removeOperator: Cant remove non-existent operator");

https://github.com/code-423n4/2021-11-nested/blob/f646002b692ca5fa3631acfff87dda897541cf41/contracts/NestedFactory.sol#L90-L90

require(address(reserve) == address(0), "NestedFactory::setReserve: Reserve is immutable");

https://github.com/code-423n4/2021-11-nested/blob/f646002b692ca5fa3631acfff87dda897541cf41/contracts/NestedFactory.sol#L97-L97

require(address(_feeSplitter) != address(0), "NestedFactory::setFeeSplitter: Invalid feeSplitter address");

https://github.com/code-423n4/2021-11-nested/blob/f646002b692ca5fa3631acfff87dda897541cf41/contracts/NestedFactory.sol#L109-L109

require(_orders.length > 0, "NestedFactory::create: Missing orders");

[adrien-supizet]

duplicate #14