this commit improves the fuzz examples for the selector table. the
nested `@given` tests too many "dumb" examples (ex. 0, 1, max_value)
when `max_examples` is not large enough. the nested `@given` strategy
can find falsifying inputs, but it requires the inner `max_examples` to
be set much higher, and the shrinking takes much longer. this setting
of `max_examples=125` with a single `@given` using the `@composite`
strategy in this commit finds the selector table bug (that was fixed in
823675a8dc) after an average of 3 runs.