Panic in `rust/examples/spin-tracing`

There's a panic that happens when attempting to alter the parent span within a function that uses the `tracing::instrument` macro:
```text
thread '' (1) panicked at examples/spin-tracing/src/lib.rs:44:9:
Span has already been started, cannot set parent
```

```rust
#[instrument(fields(my_attribute = "my-value"))]
fn main_operation() {
let wasi_propagator = opentelemetry_wasi::TraceContextPropagator::new();
if let Err(e) =
// Panics
tracing::Span::current().set_parent(wasi_propagator.extract(&Context::current()))
{
panic!("{e}");
};

tracing::info!(name: "Main span event", foo = "1");
child_operation();
}
```

This can be worked around by moving the host context extraction into the `handle_spin_tracing` method; however, this is not ideal:
```rust
// Propagate the context from the Wasm host
let wasi_propagator = opentelemetry_wasi::TraceContextPropagator::new();
let _guard = wasi_propagator.extract(&Context::current()).attach();

main_operation();
```

We need to investigate whether there is a way to set the parent span after the span has already been started.