Change machine.LiteralByte and llvm.ConstantByte to use UByte

[jiribenes]

Follow-up from #1170

Why use big number when small number do trick?

[phischu]

Yes, we should then also make core.Literal use UByte for byte literals and changes the line here:
https://github.com/effekt-lang/effekt/blob/master/effekt/shared/src/main/scala/effekt/machine/Transformer.scala#L479

[jiribenes]

That part is already done in #1170. :)