feature-flag console-subscriber

[zeroXbrock]

Describe the bug

When installing/building contender outside of the context of the workspace (i.e. cargo install) the binary will be bricked, saying it needs to be built with RUSTFLAGS="--cfg tokio_unstable". This can be fixed by running RUSTFLAGS="--cfg tokio_unstable" cargo install ... but this is annoying and should not be the default.

To Reproduce

cargo install --git https://github.com/flashbots/contender --locked
contender -V

Expected behavior

Users shouldn't need to provide special build flags to install contender. The tracing-subscriber crate is only used to log data from async tokio tasks, which is only useful for developers, who won't mind providing special build flags as much.

Feature description

• add a feature flag tokio_subscriber to contender that enables the following, which will be disabled be default:
  • installation of the console_subscriber crate
  • use of that crate (see tokio_layer in cli::init_tracing)