* add id to tracing span

* Revert "add id to tracing span"

This reverts commit 5e01e6be.

* Avoid using Span::enter() in async functions, following tracing's doc instruction https://docs.rs/tracing/latest/tracing/struct.Span.html#in-asynchronous-code

* * fixed all Span::enter()
* clean up

* fix fmt

* changed RpcTracing::span -> into_span instead of cloning the span