Need exclusive range fuzzers

I have a test where I move an item from a custom collection into another (this neccessitates changing IDs, which is why it is a special function). I generate two lists of strings to be converted into my collection and then grab a random index from the first collection to be moved into the second.

To determine the index of the item to move, I use a `percentage` fuzzer. However, the test fails because of the edge case of the percentage being 1, where `floor`ing the `List.length * percent` doesn't help and neccessitates an extra conditional to work around the edge case.

I feel like there might be a more elegant way to choose an index. But I also think that exclusive range fuzzers might be useful in other situations as well, so I thought that this use case might motivate discussion around them.