chore: add oracle scripts

The checks behind each fix ran from throwaway shell scripts. They are
now mise tasks: build a corpus from git repos, count files that match
Prettier and sort the rest by kind, shrink a file that formatting
breaks, and time the working tree against a revision in both orders.

The semantics test takes several corpora, and its event comparison
moves to tests/support, shared with an `events` example the shrink
script uses. That example replaces a debug copy committed by mistake.