* There are a few needless borrows that don't seem to be needed. I even did a quick assembly comparison and posted a q to stackoveflow on it. See [here](https://stackoverflow.com/questions/74910196/advantages-of-pass-by-ref-val-with-impl-intoiteratoritem-impl-asrefstr)
* removed several `let _ = ...` when they don't look necessary (even a few ones that were not suggested by clippy (?))
* there were a few `then(|| ctor{})` that clippy suggested to replace with `then_some(ctor{})` -- seems reasonable?
* some unneeded assignment+return - keep the code a bit leaner
* a few `writeln!` instead of `write!`, or even consolidate write!
* a nice optimization to use `ch.is_ascii_digit` instead of `ch.is_digit(10)`
This has to re-introduce the `sink` pattern, because doing this purely
with iterators is awkward :( Maaaybe the event vector was a false start?
But, anyway, I like the current factoring more -- it sort-of obvious
that we do want to keep ws-attachment business in the parser, and that
we also don't want that to depend on the particular tree structure. I
think `shortcuts` module achieves that.
