Subsystem to throw error when missing help (and other required ClassVars) #22085Description
Stems from this Slack convo: https://pantsbuild.slack.com/archives/C046T6T9U/p1741350745698019
But essentially, if someone adds a new subsystem, we require that they add a help (as we use it during pants help) - but it doesn't throw a pyright or mypy error if missing.