Add exact argument to array.zip

[T0mstone]

This adds a named argument exact: bool (default false) to array.zip that, when enabled, checks whether all given arrays are actually the same length and errors if they are not.

Motivation

I had a situation where a table was missing a row because I constructed it using array.zip and I accidentally made one of my columns shorter than the others. This lets users easily enforce the abscence of such a bug.

Alternatives

Of course, this behavior can be implemented in typst already:

let checked-zip(first, ..arrs) = {
  for arr in arrs.pos() {
    if arr.len() != first.len() {
      panic("arguments have different lengths")
    }
  }
  array.zip(first, ..arrs)
}

However, I think that this is still something important enough to warrant inclusion in the method itself,
and doing it natively also allows for better error messages.

Documentation and Tests

I haven't written tests and documentation for this yet to save on effort in case this PR is rejected. I will add them if it is approved.

[laurmaedje]

I think it makes sense to have this.

[T0mstone]

Should be good to merge now.

[T0mstone]

Ok, now it should be good.

[laurmaedje]

Thanks, looks great!