Clone state a bit less

[davidpdrsn]

This reduces the state clones by 1 for each request. Not much but better than nothing. Had to inline the call_route to get around some borrowing issues.

The remaining clones are

1. https://github.com/tokio-rs/axum/blob/main/axum/src/handler/service.rs#L171
   • I'm gonna invest making Handler::call take S by reference rather than value. Not sure what the implications are. Think the response future should still be 'static so might not be possible.
2. https://github.com/tokio-rs/axum/blob/main/axum-core/src/extract/from_ref.rs#L23
   • This one we can't do much about. Its the State extractor via FromRef. That needs to produce an owned state.
3. https://github.com/tokio-rs/axum/blob/main/axum/src/routing/route.rs#L48
   • Because of backpressure Route::call uses oneshot which requires clone. Not sure its possible to fix but worth investigating.
4. https://github.com/tokio-rs/axum/blob/main/axum/src/test_helpers/test_client.rs#L32 (when hyper calls call on Shared that clones the service)
   • Nothing we can do about this. Hyper needs an owned service to serve the connection.

Part of #1827

[davidpdrsn]

Ah okay I messed up the tests a bit. I'll fix that later 😅