Various fixes for leaving a messy git state

[pbrisbin]

The CLI was never very hygienic with the git state it leaves after a local run. As we
refactored things such that the common use case is "local" on GitHub Actions, this
became a problem. It resulted in weird PRs being created by create-pull-request
action.

These fixes should address what I've found so far.

---

Only commit paths we restyled

ed2f4dd

This avoids unintentionally including other files we may have created,
such as downloaded files or backup files produced by a restyler.

Run git-clean at the end, by default

f25f036

This ensures any files created by the restyling process are cleaned up,
which is important to prevent any create-pull-request action running
after us from including them in its own commit.

Behavior can be disabled by NO_CLEAN / --no-clean.

Prevent empty changesets when restylers offset each other

3ff33ab

Sometimes, two restylers can "fight". One changes code one way and then
another puts it exactly back. When this happens, each restyler will
generate their own commit, but the overall changeset will be empty.

If we don't explicitly check for this, using the create-pull-request
action will still produce a PR because there are commits, even if the
overall diff is empty. This empty PR might just be merged out of habit
or process, triggering the process to repeat again.

So we'll explicitly check:

• If we made changes,
• If those changes made commits
• If there's no diff against our first commit's parent ({sha}^)
• Then we'll do a git reset --hard back to it

Version bump

ba396c0