Rewrite rules for Lazy.compareLength are too lazy

`Lazy.length s` must force the entirety of `s`, while (by design) `Lazy.compareLength s 10` stops after finding at least 11 words. And yet we try to rewrite `Lazy.length s > 10` to `Lazy.compareLength s 10 == GT`. I can't quickly think of any "reasonable-looking" example where this change will actually cause problems, but I am deeply skeptical of a rewrite rule that silently changes strictness behavior in this way, especially since it is common for forcing a lazy bytestring to mean performing deferred I/O actions.

(Also, `Int64` overflow can happen in `Lazy.length` but not in `Lazy.compareLength`, though it's probably only possible to actually observe that difference in behavior by doing something rather stupid.)