Core Excubiae smart contract framework

[0xjei]

WIP

The following PR introduces the core Excubiae abstract smart contract. This contract will be used as the basis for defining custom and specific Excubia gatekeepers. It also implements the FreeForAllExcubia gatekeeper, which allows anyone to pass the check the first time. This will be useful for starting to implement tests, scripts and so on.

nb. this is a porting + refactoring + extension from https://github.com/privacy-scaling-explorations/zk-kit.solidity/tree/main/packages/excubiae

Resources to study & check

• https://book.getfoundry.sh/forge/tests
• https://book.getfoundry.sh/forge/advanced-testing
• https://hardhat.org/tutorial/testing-contracts
• https://book.getfoundry.sh/tutorials/best-practices
• https://hardhat.org/ignition/docs/guides/creating-modules
• https://consensys.github.io/smart-contract-best-practices/
• https://docs.soliditylang.org/en/latest/security-considerations.html

[ctrlc03]

Thanks!