ERC-7629: Unified Token

[abcoathup]

@sennett-lau

For DN404:
DN404 focuses on a unique approach where an entity can simultaneously own ERC20 and ERC721 tokens. This mechanism allows for the minting / burning of ERC721 tokens based on the amount of ERC20 tokens held, rather than enabling direct swapping between token types.

Now it is a proposed ERC:
ERC-7631: Dual Nature Token Pair
https://github.com/ethereum/ERCs/pull/271/files