Add `multi_token` (NEP-245) in near-contract-standards

I often use FT and NFT ext-traits from near-contract-standards, but if I want to support nep245, I have to write interfaces and methods myself, which is not the best experience. Would be nice to have more tools for work with / implementation of nep245 tokens, so that apps can benefit from interoperability with hot bridge and near intents tokens