base: Numeric: remove 'Show' constraint on 'showIntAtBase'
This MR removes the constraint Show on a few functions in Numeric.
The show usage is replaced by `show . toInteger' which is "morally" the same behavior. It only impacts the string content of an exception.
However removing the constraints makes the function (and derived functions) more generic.
Draft status, I'm submitting in order to trigger CI and see if it changes any test case.