purge str::from_utf8() from puzzle examples and use as char instead?

[Lotterleben]

participants have run into ownership & referencing/dereferincing/slice-ifying problems while re-using our use of str::from_utf8() in the past. I'm wonderin if that#s an unncessary roadblock and it'd make more sense didactically just use as char for now, even though it's not the 100% safest option