[BUG] `Rc<RefCell<wasm_bindgen_futures::Inner>>` cannot be sent between threads safely

### Is there an existing issue for this?

- [X] I have searched the existing issues

### What version of `workers-rs` are you using?

0.0.21

### What version of `wrangler` are you using?

2.13.0

### Describe the bug

I see that you have recently added an example with [axum](https://github.com/cloudflare/workers-rs/tree/main/examples/axum). This is great! It would allow use of the entire [tower](https://crates.io/crates/tower) ecosystem.

`Env` implements `unsafe Send` which is perfect. But any attempt to use it fails. I cannot figure out how to make this work with any non-trivial example. Could you please share how you imagine this should work? For example, here I have extended the example to try and list R2 objects:

```rs
use std::sync::Arc;

use axum::{extract::State, routing::get, Router};
use axum_macros::debug_handler;
use tower_service::Service;
use worker::*;

#[derive(Clone)]
pub struct AppState {
env: Arc,
}

fn router(env: Env) -> Router {
let state = AppState { env: Arc::new(env) };
Router::new().route("/", get(root)).with_state(state)
}

#[event(fetch)]
async fn fetch(
req: HttpRequest,
env: Env,
_ctx: Context,
) -> Result> {
console_error_panic_hook::set_once();
Ok(router(env).call(req).await?)
}

#[debug_handler]
pub async fn root(State(AppState { env }): State) -> &'static str {
env.bucket("BUCKET")
.unwrap()
.list()
.execute()
.await
.unwrap();
"Hello Axum!"
}
```

However, we see this is not possible:

```
error[E0277]: `Rc>` cannot be sent between threads safely
--> src/lib.rs:28:1
|
28 | #[debug_handler]
| ^^^^^^^^^^^^^^^^ `Rc>` cannot be sent between threads safely
29 | pub async fn root(State(AppState { env }): State) -> &'static str {
| --------------------------------------------------------------------------- within this `impl Future`
|
= help: within `impl Future`, the trait `Send` is not implemented for `Rc>`
note: required because it appears within the type `JsFuture`
--> /Users/creston/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wasm-bindgen-futures-0.4.42/src/lib.rs:101:12
|
101 | pub struct JsFuture {
| ^^^^^^^^
= note: required because it captures the following types: `worker::ListOptionsBuilder<'_>`, `JsFuture`
note: required because it's used within this `async` fn body
--> /Users/creston/Projects/workers-rs/worker/src/r2/builder.rs:396:51
|
396 | pub async fn execute(self) -> Result {
| ___________________________________________________^
397 | | let list_promise = self.edge_bucket.list(
398 | | js_object! {
399 | | "limit" => self.limit,
... |
420 | | Ok(Objects { inner })
421 | | }
| |_____^
= note: required because it captures the following types: `axum::extract::State`, `Arc`, `Bucket`, `impl Future>`
note: required because it's used within this `async` fn body
--> src/lib.rs:29:77
|
29 | pub async fn root(State(AppState { env }): State) -> &'static str {
| _____________________________________________________________________________^
30 | | env.bucket("BUCKET")
31 | | .unwrap()
32 | | .list()
... |
36 | | "Hello Axum!"
37 | | }
| |_^
note: required by a bound in `__axum_macros_check_root_future::check`
--> src/lib.rs:28:1
|
28 | #[debug_handler]
| ^^^^^^^^^^^^^^^^ required by this bound in `check`
= note: this error originates in the attribute macro `debug_handler` (in Nightly builds, run with -Z macro-backtrace for more info)
```

### Steps To Reproduce

1. Modify axum example with the above code to read R2 bucket
2. Observe failure to build