feat: make InitPayment support both async and non-async functions

- Updated InitPayment type to return Promise<Partial<Payment>> | Partial<Payment>
- Modified initProviderPayment hook to handle both async and sync returns using Promise.resolve()
- Enables payment providers to use either async or synchronous initPayment implementations

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/collections/hooks.ts

@@ -2,10 +2,12 @@ import type { Payment } from '../plugin/types/index'
 import type { Payload } from 'payload'
 import { useBillingPlugin } from '../plugin/index'
 
-export const initProviderPayment = (payload: Payload, payment: Partial<Payment>) => {
+export const initProviderPayment = async (payload: Payload, payment: Partial<Payment>): Promise<Partial<Payment>> => {
   const billing = useBillingPlugin(payload)
   if (!payment.provider || !billing.providerConfig[payment.provider]) {
     throw new Error(`Provider ${payment.provider} not found.`)
   }
-  return billing.providerConfig[payment.provider].initPayment(payload, payment)
+  // Handle both async and non-async initPayment functions
+  const result = billing.providerConfig[payment.provider].initPayment(payload, payment)
+  return await Promise.resolve(result)
 }