span-calculation: comment 85% CPU span calculation

[NadiaYvette]

Description

Anomalies were seen with 85% CPU span calculations. This is at least trying to figure out what's going on and explain it to everyone else. That said, it appears the trouble is most likely in emitting the traces, given what Micha just spotted instantly upon looking at it today. At the very least, the audit of the reporting calculations produced some comments even if it didn't find the bug.

This consists exclusively of adding comments to the code. There should be no runtime effects. At most I might have to fix up some new haddock warnings.

This was documentation as a by-product of an auditing/debugging effort.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. These may include:
  • golden tests
  • property tests
  • roundtrip tests
  • integration tests
    See Runnings tests for more details
• Any changes are noted in the CHANGELOG.md for affected package
• The version bounds in .cabal files are updated
• CI passes. See note on CI. The following CI checks are required:
  • Code is linted with hlint. See .github/workflows/check-hlint.yml to get the hlint version
  • Code is formatted with stylish-haskell. See .github/workflows/stylish-haskell.yml to get the stylish-haskell version
  • Code builds on Linux, MacOS and Windows for ghc-8.10.7 and ghc-9.2.7
• Self-reviewed the diff

Note on CI

This consists exclusively of adding comments, so it might at worst trigger some new haddock warnings. I'll fix whatever of those crops up, too, of course.

[NadiaYvette]

Sorry about the noise with the accidental closing & re-opening. I fat fingered a push & ended up pushing a tree identical to master over it.

[github-actions]

This PR is stale because it has been open 45 days with no activity.