feat: Add Mollie payment provider support

- Introduce `mollieProvider` for handling Mollie payments
- Add configurable payment hooks for initialization and processing
- Implement `initPayment` logic to create Mollie payments and update metadata
- Include types for Mollie integration in payments and refunds
- Update `package.json` to include `@mollie/api-client` dependency
- Refactor existing payment-related types into modular files for better maintainability

src/plugin/singleton.ts

@@ -0,0 +1,11 @@
+export const createSingleton = <T>(s?: symbol | string) => {
+  const symbol = !s ? Symbol() : s
+  return {
+    get(container: any) {
+      return container[symbol] as T
+    },
+    set(container: any, value: T) {
+      container[symbol] = value
+    },
+  }
+}