Performance: remove async-trait

[Congyuwang]

Since async trait is now stable in rust. We can think of removing relying on the the async-trait macro, which requires returning Boxed Future which is less efficient than using rust native async trait.

[taikulawo]

Unless use generic to generate nested HttpModules at compile time. Current Rust AFIT isn't dyn compatible, so Box<dyn HttpModule> not works.

[Congyuwang]

Unless use generic to generate nested HttpModules at compile time. Current Rust AFIT isn't dyn compatible, so Box not works.

Oh right, that makes sense.

[eaufavor]

We will keep this issue open but until std async trait becomes 1:1 replacement for async-trait, no action to make here