mutate: say which tests the edits were asked of the longest in all

[aledbf]

After the cost table, mutate lists the ten tests the edits cost the most: package (its directory from the module root, whether asked by directory or named by go test), how many times an edit was put to it, and for how long in all. Test processes run -v and each top-level test's end line is counted.

The cost of a run is now mostly slow tests asked once per edit. On spin's 5c3b5a8a:

  internal/controlplane/app   TestAControlPlaneStopsTheServerThenItsWorkThenItsDatabase  100×  6m22s
  cmd/controlplane/cmd        TestAStoreWaitsForWhatItRunsOn                              68×  3m59s
  cmd/controlplane/cmd/storage TestAStorageActionDoesWhatItNames                           50×  1m8s

Those go to spin as issues; this is what finds the next ones.

task test, task lint, mutate (-j 2, 0 survived): green.

🤖 Generated with Claude Code

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