[chore] minor improvements

[MangoIV]

• spelling corrections
• use tested-with stanza and get-tested
  • use get-tested by @kleidukos to extract cabal versions to test with directly from tested-with stanza
  • allow workflow_dispatch, don't waste ci minutes on cron jobs
• use implicit argument for runtime rep for better type application
  • I expect these to be used with type applications rarely, however, I think this would prevent unnecessary confusion, especially as e.g. ghci doesn't display explicit runtime reps on its own
• document the module header

I also have a question to @ekmett: is there a specific reason why the exception types are data, not newtype?

[ekmett]

The newtype thing was an accident of evolution. they started as informationless, but evolved to contain their source location, when they had no info they had to be data, and I didn't fix it when they became one field. Fixed in HEAD.