Provider-neutral payment types and the trait every kasapay adapter implements.

Nothing here talks to a network. It defines what a charge is, what an amount is, and what a failure is, so that kasapay-stripe and kasapay-iyzico can disagree about everything else.

The shape of a payment

[Provider::charge] does not return a completed payment. It returns a [Charge] with a [Status], and — where the payer still has work to do — a [NextAction]. Stripe answers a client_secret to confirm in the browser; iyzico answers a deep link into its own app. Both are the same shape here, and neither is a success yet.

Amounts

[Money] counts minor units. There is no f64 anywhere in this crate, and [Money::parse] refuses precision a currency does not have rather than rounding it away.