response.To aliases request desired state and context

`response.To` says it copies request state into the response, but it currently reuses the same `Desired` and `Context` pointers.

That means a function can mutate the original request just by updating the response after `To(...)`. This is easy to hit in normal SDK usage because functions commonly call `response.To(...)` and then add desired resources or context entries.

Repro:
1. Build a request with `Desired` and `Context`.
2. Call `rsp := response.To(req, ttl)`.
3. Mutate `rsp.Desired` or `rsp.Context`.
4. `req` changes too.

Expected: `To` should deep copy request state before returning the response.