Tracing performance issue

[aoudiamoncef]

I did a deeper research about tracing/logging in Rust and I found that it's quite similar as other languages.
We could do some hacks to improve tracing performance :

1- Update to the latest snapshot release of tracing crate which seems to fix the issue.

2- Lazy evaluate tracing statements by passing a closure to logging macro.

3- RUST_LOG or our custom env variables with and wrap it with if statement using a custom macro.

4- Split Logging from tracing to take full control of log crate. we could use tracing_log crate to get log back to tracing.

This is an issue which is quite similar to our needs :
tokio-rs/tracing#620