feat: implement optimistic locking for payment updates

- Add version field to Payment interface and collection schema
- Implement atomic updates using updateMany with version checks
- Add collection hook to auto-increment version for manual admin updates
- Prevent race conditions in concurrent webhook processing
- Index version field for performance

Co-authored-by: Bas <bvdaakster@users.noreply.github.com>

src/plugin/types/payments.ts

@@ -48,6 +48,10 @@ export interface Payment {
     | boolean
     | null;
   refunds?: (number | Refund)[] | null;
+  /**
+   * Version number for optimistic locking (auto-incremented on updates)
+   */
+  version?: number;
   updatedAt: string;
   createdAt: string;
 }