Fix layers being cloned for each request

[davidpdrsn]

I would expect #2582 to work since we no longer clone the whole router for each request (#2483).

Turns out we were missing a .with_state(()) to eagerly apply layers like we used to do for .into_ make_service(). This might also have a performance impact.

edit(jplatte): Closes #2582.

[dayvejones]

Hello! Will this PR allow the RateLimitLayer (Tower) to be used?

#2520

[jplatte]

This makes me think that there's a performance benefit to be had by having a separate RouterService again (where inner routes are known to not require state be cloned into them anymore).

Uncertain if this is actually an improvement

[jplatte]

Okay I was uncertain because of the comments in #2634 but actually David wrote that this fixes #2582 so assume it is tested. And even if it wasn't fixing anything, we have enough tests to tell that it doesn't break anything obvious.