docs: fix wait.for() idempotency example to use a single options object (#4038)

The wait.for() idempotency example passed the idempotency options as a
second argument, but wait.for() takes a single options object — so the
second object was silently ignored and the key never applied. Merged the
fields into the single options object, matching the wait.until()
example.

Supersedes #4021.

docs/wait-for.mdx

@@ -38,5 +38,5 @@ You can pass an idempotency key to any wait function, allowing you to skip waits
 
 ```ts
 // Specify the idempotency key and TTL when waiting for a duration:
-await wait.for({ seconds: 10 }, { idempotencyKey: "my-idempotency-key", idempotencyKeyTTL: "1h" });
+await wait.for({ seconds: 10, idempotencyKey: "my-idempotency-key", idempotencyKeyTTL: "1h" });
 ```