Do it all at once in preparation for Go 1.18 support.
To make this commit, I've simply modified the `fmt-check` Makefile
target to rewrite files instead of listing the differences. So this is a
fully mechanical change, it should not have introduced any errors.
This only works with a custom bossac build from Arduino, not with the
upstream version. It avoids needing the manual "double tap" to enter
bootloader mode before flashing firmware.