[Feature] Add #[worker::trait_send] for async_trait

### Is there an existing issue for this?

- [X] I have searched the existing issues

### Description

This is an ergonomics problem for when I have to implement a trait using [async_trait](https://docs.rs/async-trait/latest/async_trait/) when passing JsValues, right now in order to make it work I have to do something like

```rs
struct MyStruct {
db: D1Database
}

#[worker::send]
async fn do_foo(value: &MyStruct) {
// run logic
}

#[async_trait::async_trait]
impl SomeAsyncTrait for MyStruct {
fn foo(&self) {
do_foo(self).await;
}
}
```
Where it would be much nicer and more readable to be able to do something like this, which should probably be behind an `async_trait` feature flag
```rs
struct MyStruct {
db: D1Database
}

#[async_trait::async_trait]
impl SomeAsyncTrait for MyStruct {
#[worker::trait_send]
async fn foo(&self) {
// run logic
}
}
```

I have next to no experience in writing Rust macros, and at a quick glance there's more going on here than I'd be easily able to dig through and understand with my lacking experience, so I hope someone picks this up since we can now easily use [axum-login](https://github.com/maxcountryman/axum-login) which requires implementing async traits