Use package local metrics

[SuperQ]

Improve performance of metrics by moving them to the package that needs them. This reduces the overhead to a simple atomic increment for basic counters like cache hits/misses. This also uses promauto to avoid the second step of having to register metrics.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.91%. Comparing base (fe84ab8) to head (23ded2f).
Report is 125 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1578      +/-   ##
==========================================
+ Coverage   93.88%   93.91%   +0.03%     
==========================================
  Files          78       79       +1     
  Lines        6361     5078    -1283     
==========================================
- Hits         5972     4769    -1203     
+ Misses        300      218      -82     
- Partials       89       91       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[ThinkChaos]

LGTM, would be nice to move the other metrics too, but @0xERR0R should chime in, as mentioned in #1560, before you do more work :)

[SuperQ]

Yes, I did this PR as an example of the re-architecture. I'm happy to contribute more improvements.

[ThinkChaos]

Looks like the end to end test for metrics failed though, so it might now fully work at the moment.

EDIT: from the logs, the missing metrics match the changed ones:

  the missing elements were
      <[]string | len:2, cap:2>: [
          "blocky_cache_hits_total 0",
          "blocky_cache_misses_total 0",
      ]

[SuperQ]

Ahh, yes, this is because metrics/metrics.go creates an isolated metrics registry instead of using the standard default registry.

Also because it's not created by the main or exported it's not easy to pass the registry around.

The simplest solution would be to use the default registry.

[SuperQ]

I went another direction and simply exported the registry from the metrics package.

[0xERR0R]

👍