refactor: remove async_trait in tx builder

[onbjerg]

Motivation

Closes #268

Solution

We can't use async fn because we need the Send bound for NetworkSigner

PR Checklist

• Added Tests
• Added Documentation
• Breaking changes

[mattsse]

does this work for wasm?

[onbjerg]

unsure, but this entire crate does not yet work for wasm because of #262

[onbjerg]

ah, I assume it's not, wasm-bindgen does not generate Send futures. i assume we would need to conditionally compile this, but I'd leave that for the above issue perhaps, wdyt

[DaniPopes]

related: impl_future! macro in alloy_transport

alloy/crates/transport/src/lib.rs

Lines 61 to 65 in 86027c9

	macro_rules! impl_future {
	(<$($t:tt)+) => {
	impl (::core::future::Future<$($t)+) + Send
	};
	}