Fix duplicate keys

[agourlay]

This PR tackles the issue #15

I have already shared my analysis and findings in this comment

Adding the Ord requirement seems logical but I understand that it is a breaking change.

[jonhoo]

Thank you! So, my main concern here is actually that we'll end up producing fewer keys than expected, and so the results will no longer accurately match the expected mix 🤔 Unfortunately, we quickly run into the birthday problem here where the more keys you want, the more likely it is to hit duplicates when sampling randomly. I don't have a great solution for this... We could maybe generate sequential keys (not random) and then shuffle them instead (at least when the number of keys needed is large)?

[agourlay]

Closing due to inactivity on my side.