refactor!: remove `Core` contracts and `OwnableUnset`

[CJ42]

What does this PR introduce?

This PR is a big ♻️ refactor that aims to help simplifying the overall inheritance of the ERC725 contracts and any contract that inherit them.

⚠️ BREAKING CHANGES

• Remove the OwnableUnset contract in favour of using Ownable and OwnableUpgradeable from @openzeppelin contract libraries.

OwnableUnset is a bad architectural choice because it is an inheritance fork of Ownable from OpenZeppelin. This creates friction when inheriting these contracts with other contracts from OpenZeppelin that also inherit from Ownable or OwnableUpradeable. For instance, compiler errors around which event to pick, etc... (screenshots below)

To create less frictions, use the Ownable and OwnableUpgradeable from OZ in the ERC725 inheritance. This makes the inheritance graph easier and simpler. Other child contracts can then re-derive from the same AST node in the inheritance tree

Also note that OwnableUnset is barely used at all anywhere in eth ecosystem.

• Remove the Core contracts in favour of duplicating the core code logic between the Standard (with constructor) and InitAbstract (with _initialize(...)) functions.

📦 Build

• Upgrade OpenZeppelin contracts dependencies to latest patch release from 4.9.3 -> 4.9.6

Contract Size Difference

PR Checklist

• [x] Wrote Tests
• [x] Wrote Documentation
• [x] Ran npm run lint && npm run lint:solidity
• [x] Ran npm run format (prettier)
• [x] Ran npm run build
• [x] Ran npm run test