Would it be feasible to remove async-trait from codegen-ed server traits?

[kanpov]

Instead, the codegen could just spit out a normal trait with fn ... -> impl Future<Output = ...> + Send, and in rare cases where the server traits need object safety, there could be an opt-in option to use fn ... -> Pin<Box<dyn Future<Output = ...> + Send>> instead.

Benefits:

• Removal of a dependency
• Reduction in compilation times for pretty much all tonic-based projects since the async-trait proc macro no longer would need to be invoked by the compiler
• async_trait is no longer reexported by tonic as #[tonic::async_trait]

Drawbacks:

• Breaking change

What do you think?