[Bug] Clean up metrics feature flag

[vicsn]

🐛 Bug Report

Lower level crates enable metrics by default, making the higher level metrics feature useless. See the appended diff for an improved setup diff.txt.

This simple cleanup is not high priority by itself, but it is key that features are handled uniformly so that we don't mess up implementing consensus-critical features like test_targets

Expected Behavior

Ideally the top-level Cargo.toml has metrics in its default feature list, which can be used to enable or disable all metrics functionality