Feature gate heavy tracing dependencies

[nathanwhit]

There were some concerns raised about chalk's dependency on tracing, tracing-subscriber, and tracing-tree, particularly in how they might affect the compilation time and binary size of rust-analyzer.

This PR experimentally gates tracing-subscriber, tracing-tree, and the attributes feature of tracing behind a new feature tracing-full. The handling of the instrument attribute macro from tracing (which only works with the attributes feature enabled) is in particular a bit hacky. In order to avoid manually adding cfg_attr to each usage of the instrument macro, this PR creates a wrapper macro exported from chalk-derive which does so.

[jackh726]

I'm okay with the tracing-full feature flag, but I don't think we want to gate instrument at all.

[nathanwhit]

I'm okay with the tracing-full feature flag, but I don't think we want to gate instrument at all.

I looked into this a bit more and indeed gating instrument doesn't seem to have much of a benefit in terms of compilation time or binary size (which makes sense, the only heavy dependency it uses is syn which we already depend on).

Just pushed some changes so now we don't gate instrument.