chore: add format script

[brillout]

Not sure if I should have applied prettier to all files. Maybe we shouldn't if it potentially introduces many merge conflicts.

[brillout]

(Maybe it's simpler if Bati's source code just doesn't enforce any formatting.)

[brillout]

Now that formatting is applied everywhere, I recommend this action which runs this script.

[brillout]

Now that formatting is applied everywhere, I recommend this action which runs this script.

In order to avoid pesky merge conflicts caused by formatting.