[Clarity 4] `to-ascii?` return type is max-length

[hugoclrd]

The return type of the newto-ascii? Clarity is 1048571, the max length, causing issues like this one:

(define-read-only (get-info) {
  one: (to-ascii? u1)
})

Error: invalid tuple syntax: created a type which was greater than maximum allowed value size

Preventing the use of to-ascii? in tuples, and potentially causing issues in costs estimation (that would be too high).