Annoying way to enable Tracy profiling

[Dzmitry Malyshau]

Everything is great, except for the fact there needs to be this small line:

let _ = profiling::tracy_client::Client::start();

This line can only be done if profiling/profile-with-tracy is enabled, but cargo/rust don't have a mechanism to check for this.
The standard way to solve it is to add a feature to blade itself, such as profile-tracy. I would like to avoid this as possible - the less features we have the easier it is to configure and test.