The Request is moved into handle_request

Not including `Request` in `Response` (I don't see why it should be there) and copying `request.close_connection` allows `Request` to be moved into `handle_request`. This is useful, because it allows `Request` to be deconstructed by the server, which avoids copying of `Request` content.

Is this a desired change?
There was a reason why this was done with boxing in the past—my recollection is that it was to do with an ICE in `construct`, and when that was fixed and I unboxed things there I didn’t unbox this part. Unboxing is certainly fine now.