feat(code): Feature-gate metrics in core-consensus crate

[OakenKnight]

Closes: #681

PR author checklist

For all contributors

• Reference GitHub issue
• Ensure PR title follows the conventional commits spec

For external contributors

• Maintainers of Malachite are allowed to push changes to the branch

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.00%. Comparing base (d07ff16) to head (3a56d25).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #762      +/-   ##
==========================================
- Coverage   79.27%   79.00%   -0.27%     
==========================================
  Files         104      104              
  Lines        9026     9034       +8     
==========================================
- Hits         7155     7137      -18     
- Misses       1871     1897      +26     

Flag	Coverage Δ
integration	79.00% <100.00%> (+0.02%)	⬆️
mbt	?

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