Don't automatically enable tracing for fs feature

[ginnyTheCat]

Motivation

Currently the "fs" features is exceptional in the way that it enables tracing even if the user didn't opt into this using the "tracing" feature.

Solution

Make tracing opt-in for the "fs" feature like it is for the other features as well.

[jplatte]

I'm a bit skeptical. I think people should get these error logs if they only enable the fs feature (I suppose we could make tracing a default feature, not sure what else this would affect).

Also: tracing is a pretty common dependency in the async Rust ecosystem, can you even get around it when depending on tower-http?

[ginnyTheCat]

I think people should get these error logs if they only enable the fs feature

I agree, but errors from other modules than the fs one already support running without tracing (and not getting these error logs). I have nothing against having tracing as a default feature though.

can you even get around it when depending on tower-http

Building a http server using axum only pulls in tracing when using the tower-http fs feature or reqwest serverside (since hyper-utils's client feature still pulls it in) but client-legacy doesn't.