Add 721A token option

[jhubbardsf]

I was wondering if anyone would be interested in having a choice between the standard 721 implementation and 721A implementation? I've already played around with converting 721A to a Diamond structure and used it. With a little more work I could get it into the format that solidstate likes the code to be in. If this is something you'd be interested in having in the repo as just another option for people to use I'd be happy to do it myself.

[ItsNickBarry]

Do you mind enumerating the features included in ERC721A? I've never used it before. Is it fully compliant with ERC721?

[jhubbardsf]

ERC721A is a gas optimized ERC721 implementation originally created by Azuki to minimize batch minting costs.

https://www.erc721a.org/

It's a fully compliant ERC721, it's just optimized a little differently than the OZ implementation which most people base theirs off of.

[ItsNickBarry]

Okay, I need a list of specific features and changes, in order to determine which path makes most sense:

• Add new ERC721 extension(s) in this repository
• Publish a separate @solidstate/erc721a repository
• Take no action

In general, SS aims for composability (as far as inheritance will allow), so we need to look at how well the individual optimizations can be added as discrete features, and what fundamental compromises they entail.

[jhubbardsf]

ERC721A is functionally the same as ERC721A but with a batch mint that uses roughly the same amount of gas as a singular mint. It would make the most sense as a ERC721 Extension in this repository I would think. Incase someone had a use case for it. But open to your feedback on that.