This PR removes tokio_util::block_on - refactored compiler and file 
fetcher slightly so that we can safely block there - that's because 
only blocking path consist of only synchronous operations.

Additionally I removed excessive use of tokio_util::panic_on_error 
and tokio_util::run_in_task and moved both functions to cli/worker.rs, 
to tests module.

Closes #2960