feat: add gateway-neutral payment package

packages/payment/src/index.ts

@@ -0,0 +1,7 @@
+export * from "./types.ts";
+export * from "./store.ts";
+export * from "./database.ts";
+export * from "./core.ts";
+export * from "./adapters.ts";
+export * from "./contract.ts";
+export { paymentPlugin } from "./plugin.ts";