[RFC] Crypto/stablecoin payment plugin (Payzum)

Hi Sylius team,

I'd like to build and maintain a payment plugin for Payzum, a non-custodial crypto/stablecoin gateway (USDC/USDT, multi-chain — funds settle directly to the merchant's own wallet).

One design note up front: shop prices stay in the store's existing fiat currency — the buyer picks the crypto asset on Payzum's hosted checkout and the invoice is priced from the fiat total. So this needs no crypto currency codes in Sylius at all, which is what blocked the older cryptocurrency request in #10244.

Planned shape: a standalone plugin (SyliusPayzumPlugin) following the current payment plugin patterns (redirect to hosted checkout, webhook-driven completion with HMAC verification), built on our official PHP SDK (payzum/payzum-php), targeting Sylius 1.13/2.x.

Before I build the final packaging: would a plugin like this be welcome in the Sylius ecosystem, and do you have requirements or preferences for payment plugins (interfaces to implement, listing process)?

Disclosure: I work on Payzum and would maintain the plugin long-term.