Don't use streams and fusion

[oberblastmeister]

The documentation states

Starting from @text-1.3@ fusion is no longer implicit

However, many functions still use Stream internally, even thought they would probably run a lot faster without it. It is much more efficient to work on the underlying bytes instead of decoding and encoding to and from UTF-32 through Stream. Some functions that use Stream include cons, snoc, and isPrefix.

[Bodigrim]

I'm in favor. See also #510 (comment) for non-streaming folds.

[oberblastmeister]

I think folds should still use Stream, the issue there is that foldl should be defined as

foldl = S.foldr (flip f) z . reverseStream