feat(stays): add instant_payment to search params

Made-with: Cursor

Author: jekku

src/Stays/Stays.spec.ts

@@ -25,6 +25,7 @@ describe('Stays', () => {
       rooms: 1,
       mobile: false,
       free_cancellation_only: false,
+      instant_payment: null,
     }
 
     nock(/(.*)/)

src/Stays/StaysTypes.ts

@@ -713,6 +713,11 @@ interface CommonStaysSearchParams {
   guests: Array<Guest>
   mobile?: boolean
   free_cancellation_only?: boolean
+  /**
+   * Preview: when `true`, only pay-now (Duffel/source) rates; when `false`, only pay-at-property;
+   * when `null` or omitted, all rates. See Duffel Stays search API schema.
+   */
+  instant_payment?: boolean | null
 }
 
 export type LocationParams = {