Unchecked integer overflow of exponents in polynomial literal notation

[brianhuffman]

Cryptol silently does the wrong thing if you write a polynomial literal with an exponent that's too big to fit in an Int. For example:

Cryptol> :t <|x^^18446744073709551616|>
<| 1 |> : {n} (n >= 1, fin n) => [n]

This appears to be caused by an unsafe use of fromInteger (#637).