Add parameter-level Depot extraction

[johnpyp]

Is your feature request related to a problem? Please describe.

In Salvo, you have to imperatively call the depot.get() / depot.obtain() method to extract state from the depot, instead of being able to put it in the parameters.

Parameter state extraction makes for handlers that are easier to unit test and are somewhat less coupled to the specific framework, and do so without resorting to true global state.

Describe the solution you'd like
Axum and similar rust HTTP frameworks have State which works similarly to Depot in Salvo, except that you can do this:

async fn posts_handler(State(state): State<AppState>) {

    // use `state`...
}

instead of salvo like:

async fn posts_handler(depot: &mut Depot) {
  let state = depot.obtain::<AppState>().unwrap();
    // use `state`...
}

It would be great if Salvo could do similar parameter-level unwrapping with obtain, so we could write something like:

async fn posts_handler(Depot(state): Depot<AppState>) {

    // use `state`...
}

Describe alternatives you've considered
N/A

Additional context
N/A