Sleeping in a Spin app breaks traces

Traces are not properly emitted when a Spin app sleeps.

The commit that introduced this regression is most likely here.

e.g.

use spin_sdk::http::{IntoResponse, Response};
use spin_sdk::http_component;
use spin_sdk::observe;

/// A simple Spin HTTP component.
#[http_component]
async fn hello_world(_req: http::Request<()>) -> anyhow::Result<impl IntoResponse> {
    std::thread::sleep(std::time::Duration::from_millis(500));
    Ok(Response::new(200, "Hello, world!"))
}

Start by inspecting commit 72cc02514e3506ddda357d03d2d060d8ad08f2b1 and reproduce the issue with the Rust HTTP component shown in the report. Trace the behavior while the component sleeps, then verify that the expected traces are emitted after the sleep completes.