Migrate from Tokio, Hyper and Axum

[rvolosatovs]

Currently we rely on two different async infrastructures - tokio and async-std, which complicates usage (e.g. we sometimes need a compatibility layer) and increases our compilation times.

We have to rely on cap-async-std (https://docs.rs/cap-async-std/latest/cap_async_std/index.html), since we want to be able to run Drawbridge within as a WASI executable, therefore we should completely switch to async-std ecosystem.

We need:

• Replace Axum by some other framework, or, even better, nothing. We already do our routing manually and in many cases extract whatever is necessary from requests. Axum handlers are very difficult to debug and that slows down process. That is, however, the biggest dependency, which requires hyper and, therefore, tokio.
• Replace hyper by some other http library, probably https://docs.rs/async-h1/latest/async_h1/index.html, which is already adopted in tests https://github.com/profianinc/drawbridge/blob/53c4139d47559dd6920ad849de67324c082c5cb9/tests/mod.rs#L46-L95