This changes the test setup to use our own client rather than using
reqwest directly. Allows us to add several quality of life features like
always unwrapping results.
This way there is now only one way to create a router:
```rust
use axum::{Router, handler::get};
let app = Router::new()
.route("/foo", get(handler))
.route("/foo", get(handler));
```
`nest` was changed in the same way:
```rust
use axum::Router;
let app = Router::new().nest("/foo", service);
```
They'd previously see the nested URI as we mutated the request. Now we
always route based on the nested URI (if present) without mutating the
request. Also meant we could get rid of `OriginalUri` which is nice.
David Pedersen