Remove async-trait as dependency from crate stages

[AbnerZheng]

Refer to #6657
Replace #[async_trait] with ->imp for traits in stages: ExecuteStageTestRunner, UnwindStageTestRunner and StageExt.

[DaniPopes]

The body of the entire function should be wrapped in async move {} to preserve the same semantics. Although I don't think this matters much in this case

[mattsse]

since this is the impl of the trait, rust should be able to handle async fn here

[AbnerZheng]

yes, you're right.
Looks like impl Future + Send is only needed for pub trait, for example,

reth/crates/stages/src/stage.rs

Lines 250 to 259 in 57136e2

	pub trait StageExt<DB: Database>: Stage<DB> {
	/// Utility extension for the `Stage` trait that invokes `Stage::poll_execute_ready`
	/// with [poll_fn] context. For more information see [Stage::poll_execute_ready].
	fn execute_ready(
	&mut self,
	input: ExecInput,
	) -> impl Future<Output = Result<(), StageError>> + Send {
	poll_fn(move |cx| self.poll_execute_ready(cx, input))
	}
	}

If I use async here, the compiler throws a errors below:

error: use of `async fn` in public traits is discouraged as auto trait bounds cannot be specified
   --> crates/stages/src/stage.rs:253:5
    |
253 |     async fn execute_ready(&mut self, input: ExecInput) -> Result<(), StageError> {
    |     ^^^^^
    |
    = note: you can suppress this lint if you plan to use the trait only in your own code, or do not care about auto traits like `Send` on the `Future`
    = note: `-D async-fn-in-trait` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(async_fn_in_trait)]`
help: you can alternatively desugar to a normal `fn` that returns `impl Future` and add any desired bounds such as `Send`, but these cannot be relaxed without a breaking API change
    |
253 ~     fn execute_ready(&mut self, input: ExecInput) -> impl std::future::Future<Output = Result<(), StageError>> + Send {async {
254 |         poll_fn(|cx| self.poll_execute_ready(cx, input)).await
255 ~     } }
    |