Response::body_*blank* doesn't consume the response

Hello, just spotted my friend trying to run this in his code:
```rs
let text = res.body_string().unwrap();
let json = res.body_json::().unwrap();
```
This made me slightly confused to when would you want to await for the body twice?
I was just wondering if this has any actual use case to it, or is it just a flaw of the current implantation, because if it is just a flaw of the current implantation I would love to look in to the ways of making it more ergonomic.

My first thought was making body_*blank*() just consume the response, but if anyone dislikes this idea, I think generics & zero sized types could also be a great solution.

Start by locating the Response::body_string and Response::body_json entry points and reading how response bodies are currently consumed. Compare the existing behavior with the issue's repeated-await example, then clarify the intended API semantics and define completion with regression coverage for the chosen behavior.

Written by the indexing model from the issue text.